B    M    CHb    773 


Laboratory  Outline 
of 


Herrick&Crosby 


Second  Edition 


MEDICAL    .SCHOOL 
LIE1RAIKY 


Gift  of 
Courtney  G.  Clegg 


A   LABORATORY   OUTLINE 


of 


NEUROLOGY 


Professor 


C.  JUDSON  HERRICK,  Ph.  D. 

ssor  of  Neurologym  the  University  of  Chi 


Chicago 


and 


ELIZABETH  C.  CROSBY,  Ph.  D. 

Superintendent  of  Union  Schools,  Petersburg,  Michigan 


SECOND  EDITION,  RESET 

l'\  %•        ;  i.  •  A  •     •  •« 


PHILADELPHIA  AND  LONDON 


W.   B.   SAUNDERS   COMPANY 

1920 


Copyright,  1918,  by  W.  B.  Saunders   Company,  Revised,  Entirely 
Reset,  Reprinted,  and  Recopyrighted,  August,  1920 


Copyright,    1920,  by  W.  B.  Saunders  Company 


PREFACE  TO  THE  SECOND  EDITION 


THE  laboratory  course  in  neurology  which  is  here  outlined 
has  grown  up  in  the  University  of  Chicago  during  the  past 
twenty  years.  Many  teachers  have  participated  in  this  work 
and  all  of  these  have  contributed  something  of  value  to  the 
procedure  now  in  use.  Acknowledgments  cannot  be  made 
here  to  all  from  whom  valuable  help  has  been  received;  but 
especial  mention  should  be  made  of  the  initial  program  laid  out 
in  1900  by  Doctors  Barker  and  Kyes  when  they  were  suddenly 
confronted  with  the  problem  of  teaching  the  anatomy  of  the 
brain  to  a  very  large  class  of  medical  students  with  practically 
no  equipment  and  a  very  limited  amount  of  anatomical  material 
(see  the  paper  by  Barker  and  Kyes  cited  in  the  appended  Bib- 
liography) .  The  large  measure  of  success  which  they  attained 
should  encourage  other  teachers  whose  laboratory  equipment 
is  inadequate. 

Later  Doctors  Donaldson  and  Hardesty  elaborated  this 
course,  and  when  the  direction  of  the  work  was  assumed  by  the 
senior  author  in  1907  he  received  valuable  assistance  from  Doc- 
tor Elizabeth  H.  Dunn  in  reorganizing  the  course  into  the  form 
out  of  which  the  present  Outline  has  grown.  Professor  G.  W. 
Bartelmez  has  also  contributed  freely  from  his  own  extensive 
experience.  In  the  year  1915  the  Outline  was  thoroughly 
revised  and  privately  printed  by  the  authors.  In  the  present 
work  it  has  been  again  revised  and  recast  in  more  general  form, 
which  it  is  hoped  may  be  found  more  widely  useful. 

The  fundamental  purpose  of  the  procedure  here  outlined  is  to 
assist  the  student  as  early  in  his  course  as  possible  to  formulate 
his  knowledge  of  the  nervous  system  in  terms  of  the  functional 
significance  of  the  parts.  Free  use  has  been  made  of  the 
methods  of  functional  analysis  of  the  central  nervous  system 
which  have  been  developed,  chiefly  in  American  laboratories, 
under  the  stimulating  guidance  of  researches  upon  the  func- 
tional composition  of  the  peripheral  nerves;  and  the  experience 

5 


6  PREFACE  TO   THE   SECOND   EDITION1 

in  this  and  numerous  other  laboratories  has  demonstrated  that 
a  thoroughgoing  application  of  these  methods  is  of  the  utmost 
value  to  the  beginning  student  (cf.  Johnston,  '06  and  '08). 
In  the  senior  author's  Introduction  to  Neurology  ('18)  the 
materials  of  neurology  are  organized  from  this  standpoint  as  an 
aid  in  the  use  of  the  larger  text-books  and  atlases. 

The  course  in  neurology  here  outlined  can  be  covered  by  an 
undergraduate  class  of  properly  prepared  students  in  about 
one-half  of  a  school  year,  devoting  one  or  two  hours  each  week 
to  lecture  and  recitation  and  from  six  to  eight  hours  to  the 
laboratory.  Since,  however,  many  colleges  cannot  devote 
as  much  time  as  this  to  the  nervous  system,  the  Outline  has 
been  so  arranged  that  a  selection  can  be  made  of  those  topics 
for  which  time  and  materials  are  provided.  Students  of 
zoology  and  vertebrate  comparative  anatomy  will  naturally 
devote  more  time  to  the  earlier  parts  of  the  Outline  (sections 
3  to  60)  and  may  omit  all  of  the  work  on  the  microscopic 
structure  of  the  mammalian  nervous  system. 

For  several  years  past  there  has  been  offered  at  the  Univer- 
sity of  Chicago  a  twelve-weeks  course  in  neurology  primarily 
for  students  of  psychology  and  education  with  meager  bio- 
logical preparation.  These  students  make  a  rather  thorough 
dissection  of  the  nervous  system  of  the  dogfish,  thus  making  up 
in  some  measure  their  deficiencies  in  knowledge  of  general 
vertebrate  anatomy.  This  is  followed  by  dissection  of  the 
brain  of  the  sheep,  with  special  reference  to  some  of  the  more 
important  conduction  pathways  and  functional  centers,  such 
as  the  auditory,  optic  and  olfactory  tracts,  pyramidal  tract, 
cortical  localization,  etc.  Gross  human  material  is  freely 
used  for  demonstration.  Microscopic  sections  are  studied, 
illustrating  the  nervous  elements,  structure  of  the  sense 
organs,  spinal  cord,  cerebral  and  cerebellar  cortex,  and  if  time 
permits  a  few  of  the  conduction  pathways  within  the  brain 
stem. 

The  course  in  neurology  for  medical  students  at  the  Univer- 
sity of  Chicago  follows  the  general  histology  and  a  part,  at 
least,  of  the  gross  anatomy,  and  it  is,  in  turn,  followed  by  a 
laboratory  course  on  the  physiology  of  the  nervous  system. 
In  this  course,  which  occupies  twelve  weeks,  the  students 


PREFACE    TO    THE    SECOND   EDITION  7 

do  most  of  the  work  here  outlined  for  the  dissection  of  the 
dogfish  head  and  sheep  and  human  brains  and  for  the  study  of 
the  microscopic  sections  as  directed,  the  sections  being  sup- 
plied from  the  departmental  loan  collection.  The  "  optional 
dissections"  of  the  human  brain  (sections  102  to  111,  141  to 
152)  are  omitted,  or  are  done  by  some  students  in  extra  time 
or  in  a  more  advanced  course. 

The  second  edition  has  been  entirely  reset  and  the  references 
to  literature  brought  up  to  date.  Some  other  minor  changes 
have  been  made,  in  particular  new  blocks  for  Figures  5A 
and  5B,  which  have  been  revised  by  Norris  and  Hughes 
in  conformity  with  the  latest  results  of  their  investigations. 
Our  especial  thanks  are  due  to  them  for  their  care  in  this 
matter  and  to  numerous  others  whose  kindly  criticisms  have 
been  very  helpful. 

THE  AUTHORS. 
CHICAGO,  ILL., 
November,  1919. 


ANALYSIS  OF  CONTENTS 


PAGE 

I.  LIST  OF  RECOMMENDED  COURSES  (COURSES  I  TO  Vll) 11 

II.  GENERAL  LABORATORY  DIRECTIONS  (SECTIONS  1,  2) 13 

III.  DISSECTION  OF  THE  SHARK  (SECTIONS  3-29) 16 

IV.  THE  MAMMALIAN  NERVOUS  SYSTEM 39 

1.  Introductory  Topics  (Sections  30-40) 39 

2.  External  Anatomy  (Sections  41-60) 46 

3.  General  Directions  for  Microscopic  Material  (Sections 

61,  62) 59 

4.  Internal  Structure  of  the  Spinal  Cord  (Sections  63-68) ...  63 

5.  Sympathetic  Nervous  System  (Section  69) 67 

6.  The  Medulla  Oblongata  (Sections  70-95) 67 

7.  Structure  and  Connections  of  the  Cerebellum  (Sections 

96-100) 82 

8.  Summary  of  Spinal,  Bulbar,  and  Cerebellar  Tracts  and 

Centers  (Section  101) 89 

9.  Optional  Dissections  of  the  Brain  Stem  (Sections  102-111)  93 

10.  The  Cerebrum  (Sections  112-140) 99 

11.  Optional  Dissections  of  the  Cerebrum  (Sections  141-151).  114 

12.  Recapitulation  of  Conduction  Paths  (Sections  152,  153) . .  118 
V.  LITERATURE .  119 


LABOKATORY  OUTLINE  OF  NEUROLOGY 


I.  LIST  OF  RECOMMENDED  COURSES 

THE  materials  of  this  Outline  have  been  so  arranged  that  the 
student  may  select  any  one  of  several  methods  of  procedure 
depending  upon  the  purposes  of  the  study  and  the  time  and 
material  at  command.  The  following  courses  are  suggested. 

COURSE  I.  Comparative  anatomy  of  the  vertebrate  nervous 
system.  Gross  anatomy. — Begin  with  the  dissection  of  the 
dogfish  (sections  1  to  29).  Other  inframammalian  types  may 
be  dissected  according  to  the  same  general  plan.  Johnston's 
Nervous  System  of  Vertebrates  ('06)  should  be  read  as  a  guide 
in  these  studies;  also  the  comparative  anatomies  of  Kingsley 
('17),  Wiedersheim  ('07),  and  others.  For  the  mammalian 
nervous  system  follow  the  precedure  outlined  beyond  for  the 
sheep  (sections  30  to  59,  69  to  72,  81,  93,  95,  96(a),  100,  112  to 
117,  119  to  139).  Other  mammalian  brains  may  be  dissected 
in  the  same  way. 

COURSE  II.  Comparative  anatomy  of  the  vertebrate  nervous 
system.  Microscopic  anatomy. — After  the  completion  of  the 
gross  study  of  one  or  more  vertebrate  types  as  directed  in  the 
preceding  paragraph,  the  microscopic  study  of  the  same  types 
may  be  taken  up.  Directions  for  the  microscopic  study  of  the 
brains  of  Ichthyopsida  and  Sauropsida  are  not  included  in  this 
Outline,  and  indeed  this  study  is  tedious  and  rather  difficult 
for  the  beginner. except  under  skilled  personal  direction.  Sug- 
gestions for  microscopic  studies  of  these  types  are  given  in 
Johnston's  book  ('06).  For  the  microscopic  study  of  the 
brains  of  the  rabbit  and  cat  the  atlases  of  Winkler  and  Potter 
('11  and  '14)  are  invaluable. 

COURSE  III.  Gross  anatomy  of  the  mammalian  brain.  Short 
course. — For  a  short  course,  follow  the  procedure  directed  for 
Course  I,  omitting  the  dogfish  dissection.  Use  the  brain  of  the 

11 


12  LABORATORY   OUTLINE    OF   NEUROLOGY 

sheep,  beef,  dog,  or  cat  as  directed  in  sections  30  to  59,  69  to  72, 
81,  93,  95,  96(a),  100,  112  to  117,  119  to  139. 

COURSE  IV.  Gross  anatomy  of  the  mammalian  brain.  Longer 
course. — For  a  longer  course,  after  the  completion  of  Course 
III,  additional  vertebrate  types  may  be  used,  and  the  human 
brain  may  be  thoroughly  dissected  as  directed  in  sections  102 
to  111,  141  to  152. 

COURSE  V.  Gross  anatomy  of  the  human  brain. — Follow 
through  on  the  human  brain  the  directions  given  for  the  brain 
of  the  sheep  in  sections  30  to  59,  69  to  72,  81,  83,  95,  96(a),  100, 
112  to  117,  119  to  139.  For  a  more  extensive  course,  add  on  a 
second  specimen  the  " optional  dissections,"  sections  102  to 
111,  141  to  152. 

COURSE  VI.  Gross  and  microscopic  anatomy  of  the  human 
brain. — If  it  is  desired  to  make  a  thorough  study  of  the  human 
brain  only,  follow  the  directions  given  in  sections  30  to  153, 
with  or  without  the  " optional  dissections"  (sections  102  to  111, 
141  to  152),  using  human  material  throughout. 

COURSE  VII.  The  course  for  medical  students  at  the  Univer- 
sity of  Chicago  follows  the  Outline  substantially  as  given  in 
the  following  pages,  omitting  all  of  the  "  optional  dissections" 
(sections  102  to  111,  141  to  152)  and  a  few  other  sections,  the 
details  varying  somewhat  from  year  to  year. 


H.  GENERAL  LABORATORY  DIRECTIONS 

1.  The  laboratory  course  here  outlined  includes  the  dissec- 
tion of  the  nervous  systems  of  several  vertebrate  types,  includ- 
ing man,  and  the  microscopic  study  of  selected  portions  of 
the  human  brain  and  sense  organs.     If  microscopic  prepara- 
tions of  the  human  nervous  system  are  not  available,  those 
from  other  mammals  will  answer  very  well  for  most  purpo  es. 
Each  student  should  provide  himself  with  scalpels,  scissors, 
forceps,  drawing  paper  and  pencils  and  one  or  two  orange-wood 
or  bone  manicure  sticks  for  blunt  dissection  and  teasing  of 
brain  tissue.     Compound  microscopes  must  be  provided.     A 
simple  magnifying  lens  is  also  necessary  for  low-power  exami- 
nation of  microscopic  sections.     (For  the  requirements  of  this 
course  the  eyepiece  of  the  compound  microscope  makes  a 
satisfactory  substitute  for  a  dissecting  lens.     Hold  the  slide  to 
the  light  and  examine  it  through  the  inverted  ocular.) 

2.  The  point  of  view  from  which  this  Outline  has  been  pre- 
pared is  the  same  as  that  of  the  senior  author's  Introduction  to 
Neurology  (Philadelphia,  1918),  and  it  is  assumed  that  this 
book  is  available  for  study  throughout  the  course,  frequent 
references  being  made  to  it  in  lieu  of  full  descriptions  in  the 
Outline.     The  first  seven  chapters  of  this  work  should  be  read 
early  in  the  course  to  give  the  necessary  background  for  the 
laboratory  work.     The  illustrations  in  Burkholder's  Anatomy 
of  the  Brain  (second  edition,  Chicago,  1912)  will  be  found  very 
helpful  in  the  study  of  the  brain  of  the  sheep.     Other  reference 
books  will  be  cited  throughout  the  text.     The  titles  of  these 
works  are  assembled  in  the  Bibliography  at  the  end  and  the 
works  are  referred  to  in  the  text  simply  by  the  author's  name 
followed  by  the  date  of  publication.     Constant  use  must  be 
made  of  standard  text-books  and  atlases  of  the  gross  and 
microscopic  anatomy  of  the  human  nervous  system.     The 
following  list  includes  some  of  the  works  of  special  value  for 
this  purpose: 

13 


14  LABORATORY    OUTLINE    OF   NEUROLOGY 

Bailey  and  Miller,  Embryology  ('16). 
Bailey,  Histology,  5th  edition  ('16). 
Barker,  Nervous  System  f  01). 
Bruce,  Atlases  ('92  and  '01). 

Cunningham,  Anatomy,  Revised  4th  edition  ('15). 
Edinger,  Nervose  Zentralorgane,  8th  edition,  Bd.  I  ('11). 
Flatau,  Atlas  ('99). 

Van  Gehuchten,  Systeme  Nerveux,  4th  edition  ('06). 
Gray,  Anatomy  ('18). 
Herrick,  Introduction  to  Neurology  ('18). 
Howell,  Physiology,  7th  edition  ('18). 
Johnston,  Nervous  System  ('06). 
Luciani,  Physiology  ('15). 
Marburg,  Atlas  C04). 

Morris,  Anatomy,  5th  edition,  part  III  ('14). 
Obersteiner,  Nervose  Zentralorgane,  5th  edition  f'12).~ 
Piersol,  Anatomy  ('16). 
Quain,  Anatomy,  llth  edition  ('09). 
Ram6n  y  Cajal,  Systeme  Nerveux  ('09-'ll). 
Rauber-Kopsch,  Lehrbuch  ('12). 

Reference  Handbook  of  the  Medical  Sciences,  3d  edition,  articles  on 
the  Brain,  Cranial  Nerves,  Ear,  End-organs,  Spinal  Cord,  and  others. 
Sabin,  Atlas  ('01). 
Sobotta  ('11). 
Spalteholz,  Atlas  ('09). 
Starling,  Physiology  C15). 
Stewart,  Physiology  ('18). 
Toldt,  Atlas  ('04). 

\illiger,  Brain  and  Spinal  Cord  ('12). 
Winkler  and  Potter,  Atlases  ('11  and  '14). 

On  technical  methods  for  the  study  of  the  nervous  system 
consult  the  following  works: 

Guyer,  Animal  Micrology,  2d  edition  ('17). 

Hardesty,  Neurological  Technique  |/02). 

Hardesty,  Laboratory  Guide  for  Histology  ('08). 

Lee,  Arthur  Bolles,  Microtomist's  Vade-Mecum,  7th  edition  ('13). 

On  the  preparation  of  laboratory  drawings  and  scientific 
illustrations  for  publication  see — 

Hardesty,  Laboratory  Guide  for  Histology,  pp.  1-30  ('08). 
Guyer,  Animal  Micrology,  2d  edition,  pp.  159-172  ('17). 

A  few  of  the  leading  neurological  journals  are  listed  below. 
Neurological  articles  are  found  also  in  other  journals  of 
anatomy,  physiology,  and  medicine: 

Annali  di  Nevrologia,  Naples. 

Brain,  London. 

Folia  Neurobiologica,  Haarlem. 


GENERAL   LABORATORY   DIRECTIONS  15 

Journal  de  Neurologie,  Paris  (chiefly  clinical  neurology). 
Journal  f  iir  Psychologic  und  Neurologie,  Leipzig. 
Journal  of  Comparative  Neurology,  Philadelphia. 
Le  Nevraxe,  Louvain  (died  in  the  martyrdom  of  Belgium). 
Monatsschrift  fur  Psychiatric  und  Neurologie,  Berlin. 
Neurologisch.es  Centralblatt,  Leipzig. 

The  neurological  literature  for  each  year  beginning  With  1897 
is  listed  and  abstracts  of  the  more  important  articles  are  given 
in  the  Jahresbericht  iiber  die  Leistungen  und  Fortschritte  auf 
dem  Gebiete  der  Neurologie  und  Psychiatric  (Berlin) .  Numer- 
ous other  periodical  neurological  bibliographies  are  given  in  the 
Index  Medicus  (Washington) ,  Index  Catalogue  of  the  Library 
of  the  Surgeon  General's  Office  (Washington),  Anatomischer 
Anzeiger  (Jena),  Centralblatt  fur  Physiologic  (Leipzig),  and 
elsewhere. 

In  this  Outline  the  student's  attention  is  directed  especially 
to  those  neurological  facts  which  are  well  established  and  which 
are  of  special  significance  for  the  practical  understanding  of  the 
working  of  the  nervous  system  in  health  and  disease.  Many 
equally  interesting  features  are  not  referred  to  at  all;  and  it 
should  especially  be  borne  in  mind  that  the  topics  selected  are 
for  clearness  presented  in  as  schematic  a  way  as  possible.  The 
actual  relations  are  in  all  cases  far  more  complex,  and  many  of 
these  details  are  as  yet  imperfectly  understood.  The  student 
is  urged  to  read,  as  far  as  time  permits,  the  larger  manuals  of 
neurology  and  the  special  articles  in  the  research  journals  in 
order  to  get  the  simpler  and  more  elementary  features  of  the 
laboratory  study  in  their  proper  perspective.  This  reading 
should  be  done  topically.  As  each  section  of  the  Outline  is 
studied  in  the  laboratory,  the  topic  there  under  consideration 
should  be  read  up  as  completely  as  possible  from  both  the 
anatomical  and  the  physiological  standpoints.  After  some 
practice  in  this  sort  of  topical  reading,  with  the  aid  of  the  in- 
dexes of  the  works  consulted,  a  large  number  of  books  can  be 
abstracted  for  each  topic  with  small  expenditure  of  time. 


HI.  DISSECTION  OF  THE  SHARK 

3.  This  Outline  has  been  prepared  for  use  with  either  the 
smooth  dogfish,  Mustelus  canis,  or  the  spiny  dogfish,  Squalus 
acanthias.     It  may  be  adapted  with  very  slight  modifications 
to  the  skate  or  any  other  elasmobranch.     The  brains  and 
peripheral  nerves  of  the  different  sharks,  skates,  and  rays  ex- 
hibit minor  differences;  but  these  are  not  significant  for  the 
purposes  of  this  study. 

4.  Literature. — Laboratory  directions  for  the  general  dissec- 
tion of  the  dogfish  are  given  by  Kingsley  ('07),  Marshall  and 
Hurst  ('99),  and  for  the  allied  skate  by  T.  J.  Parker  ('00). 
Good  figures  of  the  brain  of  the  shark  are  found  in  Parker  and 
HaswelFs  Zoology  ('10,  vol.  2,  pp.  158-160),  in  Wiedersheim's 
Comparative  Anatomy  ('07,  p.  209)  and  in  Kingsley's  Com- 
parative Anatomy  ('17,  p.  185). 

On  the  structure  and  functions  of  the  sense  organs  of  fishes 
the  following  works  may  be  consulted:  Bateson  ('90);  Berger 
('82),  Ewart  ('93);  Garman  ('88),  Herrick  ('03,  '03a,  '08); 
Johnson  ('17) ;  Lee  ('98) ;  Norris  and  Hughes  ('19) ;  Parker  and 
others  ('03-'18);  Peabody  ('97);  Sheldon  ('096,  '11). 

5.  The  chief  purpose  of  the  dissection  of  the  fish,  as  outlined 
in  the  following  sections,  is  to  secure  a  clear  understanding  of 
the  relations  between  the  brain  and  the  other  organs  of  the 
body.     In  the  fish  the  brain  shows  a  series  of  enlargements 
each  of  which  is  directly  connected  by  means  of  nerves  with  a 
particular  peripheral  organ :  the  olfactory  bulbs  with  the  nose, 
the  optic  lobes  with  the  eyes,  the  acoustic  area  and  cerebellum 
with  the  internal  ear,  the  visceral  lobe  with  taste  buds,  and  so 
on  (see  Fig.  2  and  Herrick,  '18,  Chap.  VII).     In  the  medulla 
oblongata  of  this  fish  there  is  a  series  of  longitudinal  ridges, 
each  of  which  is  connected  with  a  specific  type  of  peripheral 
end-organs:  dorsally  is  the  somatic  sensory  column,  ventrally 
the  somatic  motor  column,  and  between  these  the  visceral 
sensory  and  motor  columns.     Here  are  located  the  cerebral 
centers  of  important  reflex  systems  (see  Figs.  2  and  6,  Section 

16 


DISSECTION   OP  THE   SHARK  17 

23,  and  Herrick,  '18,  Fig.  68).  The  somatic  sensory  and 
motor  systems  enable  the  animal  to  react  appropriately  to 
external  stimuli;  the  visceral  sensory  and  motor  systems  effect 
the  internal  adjustments  of  the  body,  such  as  swallowing, 
respiration,  digestion,  etc. 

The  fish  brain  can  be  clearly  seen  to  owe  its  form  to  its  physio- 
logical connections  with  peripheral  organs.  We  shall  see  that 
similar  functional  factors  are  present  in  shaping  the  form  of  the 
human  brain,  though  much  obscured  by  the  elaboration  of 
higher  correlation  centers  in  the  thalamus,  cerebral  cortex,  etc. 
In  most  respects  there  are  instructive  resemblances  between 
the  adult  fish  and  the  human  embryo  at  an  early  age  when  gill 
pouches  are  present  (see  Herrick,  '18,  Figs.  68,  69  and  70). 

6.  Examine  carefully  the  external  form  of  the  head,  noting 
particularly  the  disposition  of  the  sense  organs  and  apertures — 
mouth,  nostrils,  gills,  spiracles  (vestigial  gills),  endolymphatic 
ducts  (two  minute  apertures  near  the  midline  between  the 
spiracles,  by  which  the  internal  ears  communicate  with  the 
exterior) .    Notice  numerous  small  pores  distributed  in  the  skin. 
These  are  the  openings  of  subcutaneous  sense  organs,  which  are 
found  only  in  fishes  and  amphibians  and  are  termed  lateral  line 
organs.    There  are  two  series  of  these,  the  ampullae  of  Lorenzini 
and  the  lateral  line  canals.     The  former  are  arranged  irregu- 
larly; the  latter  comprise  four  tubes  embedded  in  the  deep 
layer  of  the  skin:  supra-orbital,  infra-orbital,  hyomandibular 
lines,  and  the  lateral  line  of  the  trunk  (see  Fig.  4).     On  the 
lateral  line  canals  see  further  in  Section  18. 

7.  First  open  the  pericardial  chamber  by  a  medial  ventral 
incision  from  the  lower  end  of  the  specimen  forward  to  the 
lower  jaw.     Note  the  two-chambered  heart,  the  ventral  aorta, 
and  the  branches  of  the  latter  to  the  gills  (aortic  arches) .     Now 
complete  the  ventral  incision  dorsalward  through  the  lower 
jaw  and  floor  of  the  pharynx,  opening  up  the  entire  length  of 
the  mouth  cavity  back  to  the  esophagus,  and  spread  laterally 
the  ventral  walls  of  the  pharynx  to  expose  the  inner  surfaces  of 
the  gills.     Next  dissect  off  the  skin  of  the  right  side  of  the  speci- 
men in  the  gill  region,  in  each  gill  noting  the  cartilaginous  gill 
arch,  the  feathery  gills,  the  firm  gill  rakers,  the  mode  of  attach- 
ment of  the  gills  to  the  skull,  and  the  clefts  between  the  gills. 

2 


18 


LABOEATOEY    OUTLINE    OP   NEUEOLOGY 


Examine  the  gills  and  determine  how  they  work  as  organs  of 
respiration,  noting  the  direction  of  flow  of  water  through  them 
and  the  mechanism  by  which  this  flow  is  maintained. 


spt.r 
7tt/.mncl.18t 


FIG.  1. — Dissection  of  the  brain  and  cranial  nerves  of  the  dogfish,  Scyllium 
catulus.  The  right  eye  has  been  removed.  The  cut  surfaces  of  the  carti- 
laginous skull  and  spinal  column  are  dotted.  cZ.l-cZ.5,  Branchial  (gill)  clefts; 
ep.,  epiphysis;  exl.rect.,  external  rectus  muscle  of  the  eyeball;  gl.ph.,  glosso- 
pharyngeal  nerve;  hor.can.,  horizontal  semicircular  canal;  hy.mnd.VII, 
hyomandibular  branch  of  the  facial  nerve;  inf. obi. ,  inferior  oblique  muscle; 
int.rect.,  internal  rectus  muscle;  lat.vag.,  lateral  line  branch  of  the  vagus  nerve; 
mnd.V,  mandibular  branch  of  the  trigeminal  nerve;  mx.V,  maxillary  branch 
of  trigeminus;  olf.cps.,  olfactory  capsule;  oZ/.s.,  olfactory  sac;  oph.V.VII, 
superficial  ophthalmic  branches  of  the  trigeminal  and  facial  nerves;  path., 
trochlear  nerve  (patheticus) ;  pl.VII,  palatine  branch  of  facial  nerve;  s.obl., 
superior  oblique  muscle;  sp.,  spiracle;  sp.co.,  spinal  cord;  spir.,  spiracle; 
s.rect.,  superior  rectus  muscle;  vag.,  vagus  nerve;  vest.,  vestibule.  (After 
Marshall  and  Hurst,  from  Parker  and  Haswell's  Zoology.) 

8.  Cut  through  the  skin  in  the  middorsal  line  and  reflect  it  on 
the  right  side  as  a  lateral  flap,  leaving  this  flap  attached  at  the 
lateral  border  of  the  head.  Locate  again  the  pores  of  the  endo- 


DISSECTION   OF  THE    SHARK  19 

lymphatic  ducts  and  avoid  injury  to  these  ducts.  Now  remove 
the  cartilaginous  roof  of  the  brain  of  the  right  side,  beginning  at 
the  opening  which  you  will  find  already  made  by  a  cut  between 
the  eyes  and  shaving  off  the  cartilage  in  thin  slices. 

9.  The  internal  ear  lies  embedded  within  the  cartilage  behind 
the  eyes  close  to  the  medulla  oblongata  under  the  pores  of  the 
endolymphatic  ducts  (see  Fig.  1).  The  semicircular  canals  of 
the  ear  can  be  seen  through  the  translucent  cartilage.  The 
three  canals  should  be  exposed  by  dissecting  away  the  sur- 
rounding cartilage,  leaving  the  membranous  canals  in  place. 
Demonstrate  the  ampullae  of  the  semicircular  canals  and  the 
connections  of  each  canal  with  the  utriculosaccular  chamber. 
Note  the  planes  in  which  the  canals  lie  in  relation  both  to  each 
other  and  to  the  long  axis  of  the  body  (cf .  the  human  relations, 
Herrick,  '18,  Fig.  85). 

Draw  the  dissection  of  the  membranous  labyrinth  at  this 
stage  of  the  dissection  without  removing  it  from  the  head.  The 
shape  of  the  utriculosaccular  chamber  can  best  be  seen  while  it 
is  still  in  place,  for  its  delicate  walls  collapse  when  removed. 
The  semicircular  canals  open  freely  into  the  dorsal  part  of  the 
common  utriculosaccular  chamber,  which  accordingly  corre- 
sponds with  the  human  utriculus.  In  well  preserved  speci- 
mens the  recessus  utriculi  with  its  sense  organ  (macula  utriculi) 
may  be  seen  lying  ventrally  of  the  superior  and  horizontal 
ampullae.  The  ventral  part  of  the  common  chamber  corre- 
sponds with  the  human  sacculus  and  in  life  contains  a  large 
ear  stone  or  otolith,  which  is  usually  disintegrated  in  the 
formalized  specimens.  In  the  wall  of  the  sacculus  there  is  a 
large  sensory  area,  the  macula  sacculi.  There  is  no  cochlea; 
but  from  the  sacculus  a  small  pouch  extends  caudo-ventral- 
ward.  This  is  the  lagena,  which  contains  a  sensory  area,  the 
macula  lagenae,  and  represents  the  rudiment  from  which  the 
cochlea  of  higher  animals  has  been  developed.  Through 
the  translucent  walls  of  the  membranous  labyrinth  the  whitish 
sensory  areas  can  be  seen  (maculae  and  cristae),  and  by  a  little 
further  dissection  the  branches  of  the  VIII  nerve  to  all  of  these 
sensory  areas  can  be  demonstrated.  The  entire  membranous 
labyrinth  may  no w  be  removed .  C  ompare  the  internal  ear  of  the 
dogfish  with  that  of  man  (see  diagram  in  Herrick,  '18,  Fig.  91). 


20 


LABORATORY    OUTLINE    OF   NEUROLOGY 


Olfactory  bulb 


Superficial 

ophthalmic  ner/e 
Deep  opVthalmic 
nenre 

laxillaru  nen/e 
iibunr  nerVe 


JBelWeen  brain 

ITidbrain 
rode 

Acoustico- 
lateral  area 

ner/e 

Skin  area 
rth  toitrlcle 


lyorjiandibular 
nerv/e 


FIG.  2. — Diagram  of  brain  and  cranial  nerves  of  the  dogfish,  Squalus  acan- 
thias,  from  above.  Natural  size.  Olfactory  part  of  the  brain  is  marked  with 
coarse  dots,  the  visual  apparatus  with  crosses,  the  acousticolateral  nerves  and 
centers  with  broken  oblique  lines,  the  visceral  sensory  nerves  with  horizontal 
lines,  the  general  cutaneous  nerves  with  vertical  lines,  and  the  visceral  motor 
nerves  with  black  and  white  rectangles. 


PLATE  I 


Cut  surface  of 
cerebellum 

Acousticolateral 

area 
Dorsal  lateral 

line  root  VII 

Acousticolateral 


Acoustic  nerve  VIII 
Skin  area 
IX  nerve 

Visceral  sensory  area 
Lateral  nerve  X 
Visceral  motor  area 
Somatic  motor  area 


The  medulla  oblongata  of  Squalus  acanthias  seen  from  above  after  removal 
of  membranous  roof  of  fourth  ventricle;  X  2.  On  the  right  side  the  nerve  roots 
and  functional  areas  of  the  brain  are  designated  by  the  same  conventional  mark- 
ings as  in  Figs.  2  and  3. 


DISSECTION    OF    THE    SHARK  21 

Very  complete  descriptions  and  figures  of  the  ears  of  different 
species  of  fishes,  including  the  dogfish,  are  given  by  Retzius 
('81).  On  the  functions  of  the  ears  of  fishes,  see  the  papers  by 
F.  S.  Lee  and  G.  H.  Parker  cited  in  the  Bibliography.  For  the 
mammalian  ear  see  Section  80. 

10.  Remove  the  cartilaginous  walls  of  the  cranium  down  to 
the  foramina  of  the  cranial  nerves.  This  can  best  be  done  by 
cutting  the  cartilage  away  in  thin  slices  with  a  sharp  knife. 
The  foramen  of  the  slender  IV  nerve  will  be  first  exposed,  lying 
medially  of  the  eyeball  and  far  dorsally.  The  other  foramina 
lie  farther  ventrally. 


sticp-lateral  area 
Kin  area 


Hfuctory  bulb 

Optic  nerVe- 

Supraorbital  trunK 
Deep  ophthalmic  neiYe 
Infraorbital  trun 

FIG.  3. — The  brain  of  Squalus  acanthias  seen  from  left  side.     Designation  of 
nerve  roots  and  brain  centers  the  same  as  in  Fig.  2. 

11.  Note  the  membranes   (meninges)   of  the  brain.     The 
dogfish  brain  is  closely  enveloped  by  a  single  membrane.     Be- 
tween this  and  the  perichondrium  which  lines  the  cartilaginous 
cranium  is  a  very  loose  arachnoidal  tissue  which  is  not,  how- 
ever, condensed  into  a  definite  arachnoid  membrane,  as  in 
mammals  (cf.  Section  45). 

12.  Carefully  dissect  out  the  cranial  nerves  and  eye-muscles  of 
the  right  side.     The  optic  nerve,  eye-muscles,  and  eye-muscle 
nerves  (III,  IV,  and  VI  pairs)  are  arranged  practically  as  in 
the  human  body.     Consult  your  anatomies  for  names  and  de- 
scriptions and  determine  the  action  of  each  of  the  eye-muscles. 
Notice  the  long  ciliary  nerves  distributed  to  the  eyeball  and 
trace  their  connections,  if  possible,  with  branches  of  the  third 
and  fifth  nerves. 


22  LABORATORY   OUTLINE   OF   NEUROLOGY 

DESCRIPTION  OF  FIGURES  4,  5A,  AND  5B 

These  drawings  .illustrating  the  arrangements  of  the  cranial  nerve  com- 
ponents and  ganglia  of  the  dogfish  were  prepared  for  us  by  Dr.  H.  W.  Nor- 
ris  and  Miss  S.  P.  Hughes,  of  Grinnell,  Iowa.  They  are  based  on  an  inves- 
tigation of  the  cranial  nerve  components  of  Squalus  acanthias  by  recon- 
struction from  serial  microscopic  sections.  The  material  used  is  advanced 
embryos  ("pup"  stage),  and  is  probably  in  all  essential  respects  similar  to 
the  adult  form.  The  structures  are  drawn  as  seen  in  flat  projection  on  the 
median  plane  and  all  details  shown  are  drawn  true  to  scale  except  as  noted. 
The  completed  research  upon  which  these  drawings  are  based  has  been 
published  in  the  Journal  of  Comparative  Neurology,  vol.  xxxi,  1920,  pp. 
293-402,  under  the  title  "The  Cranial,  Occipital,  and  Anterior  Spinal 
Nerves  of  the  Dogfish,  Squalus  acanthias."  (This  is  the  article  referred  to 
in  the  text  and  Bibliography  as  Norris  and  Hughes,  1919.) 

FIG.  4. — Diagram  of  the^lateral  line  canals  and  their  nerves  of  Squalus 
acanthias,  seen  from  the  side.  The  ventral  portion  of  the  infra-orbital 
canal  is  represented  as  swung  ventro-laterally  out  of  its  true  relation  to 
the  other  structures.  The  lateral  line  canals  and  their  nerves  are  drawn 
as  they  are  developed  in  the  advanced  embryo  ("  pup  "  stage).  The  exact 
number  of  terminal  branches  of  the  lateral  line  nerves  supplying  the  canals 
is  indicated  in  the  drawing.  The  dots  at  the  ends  of  the  branches  indicate 
the  points  where  they  enter  the  canals.  They  do  not  represent  separate 
sense  organs  within  the  canals  (neuromasts),  such  as  are  found  in  most 
other  fishes.  For  the  form  of  the  sensory  epithelium  in  these  canals,  see 
the  figures  given  by  Johnson  ('17).  The  ampullae  of  Lorenzini  are  not 
indicated,  but  a  few  of  the  large  nerve  trunks  supplying  ampullae  ex- 
clusively are  shown  (a). 

ABBREVIATIONS 

a,  large  nerve  branches  supplying  ampullae  of  Lorenzini  only. 

buc.  VII,  ramus  buccalis  VII,  supplying  the  greater  part  of  the  infra-orbital  canal. 

chmd.,  canalis  hyomandibularis,  innervated  by  ramus  mandibularis  externus  VII. 

cinfro.,  canalis  infra-orbitalis,  innervated  by  rami  buccalis  VII  and  oticus  VII. 

clat.,  canalis  lateralis  (main  canal  of  the  trunk),  innervated  by  rami  supratemporalis 
X,  dorsalis  X,  and  lateralis  X. 

cmd.,  canalis  mandibularis,  innervated  by  ramus  mandibularis  externus  VII. 

cspro.,  canalis  supra-orbitalis,  innervated  by  ramuc  ophthalmicus  superficialis  VII. 

cspt.,  canalis  supratemporalis  (commissural),  innervated  by  ramus  supratemporalis  X. 

ct.,  canalis  temporalis  (anterior  end  of  main  lateral  canal),  innervated  by  ramus 
supratemporalis  IX. 

dors.X,  ramus  dorsalis  X,  supplying  about  four  end-branches  to  the  main  lateral  canal 
of  the  trunk. 

lat.  X,  ramus  lateralis  X  (main  lateral  line  nerve  of  the  trunk),  supplying  the  greater 
part  of  the  lateral  canal  of  the  trunk. 

mde.  VII,  ramus  mandibularis  externus  VII,  supplying  the  hyomandibular  and  man- 
dibular  canals. 

os.  VII,  ramus  ophthalmicus  superficialis  VII,  supplying  the  supra-orbital  canal. 

ot.  VII,  ramus  oticus  VII,  supplying  about  six  end-branches  to  the  posterior  end  of 
the  infra-orbital  canal. 

spt.  IX,  ramus  supratemporalis  IX,  supplying  three  end-branches  in  the  temporal 
canal. 

spt.  X,  ramus  supratemporalis  X,  supplying  the  supratemporal  canal  and  about  six 
end-branches  in  the  anterior  part  of  the  main  lateral  canal. 

VIII,  nervus  acusticus. 


FIG.  4. 


23 


£[[lj  Ganglia. 

p—  |  Somatic  sensory  nerves. 


Lateral  line   and  VIII 
nerves. 

Visceral  sensory  nerves. 


D  Lat 
nerves. 


Visceral  motor  nerves. 
Somatic  motor  nerves. 


nasal 


buc.VII,  ramus  buccalis  VII. 

cht.  VII,  chorda  tympani  VII. 

cil.a,  anterior  ciliary  nerve. 

oil. p.,  posteror  ciliary  nerves. 

dors.X,  ramus  dorsalis  X. 

hybr.    (occ.    l  +  2,sp.l,   2,  3),  nervus  hypo- 

branchialis. 
hy.  VII,  ramus  hyoideus  VII. 

II,  nervus  opticus. 

III,  nervus  oculomotorius. 

IV,  nervus  trochlearis. 

IXr,  roots  of  glossopharyngeus. 


ABB 

lat.X,  ramus  lateralis  X. 

max.  V,  ramus  maxillaris  V. 

mde.  VII,  ramus  mandibularis  externus  VI 

mdi.  VII,  ramus  mandibularis  internus  VI 

md.  V,  ramus  mandibularis  V. 

n.  term,  nervus  terminalis. 

occ. 1+2,  occipital  nerves. 

op.V,  ramus  ophthalmicus  profundus  V. 

os.  V,  ramus  ophthalmicus  superficialis  V. 

os.  VII,  ramus  ophthalmicus  superncialis^ 

pal.  VII,  ramus  palatinus  VII. 

ph. IX,  ramus  pharyngeus  IX. 


FIG.  5 A. — Distribution    of    the    nerve   components  in  Squalus  acanthias,  seen   from 
broken  lines.      The  functional  composition  of  the  nerves  is 

24 


TIONS 

ph.X.l-4,  first  to  fourth  ramus  pharyngeus 
X. 

prt.IX,  ramus  pretrematicus  IX. 

prt.Xl-4,  first  to  fourth  ramus  pretrema- 
ticus X. 

pst.IX,  ramus  posttrematicus  IX. 

pst.Xl-4,  first  to  fourth  ramus  posttrema- 
ticus X. 

sp.1-6,  first  to  sixth  spinal  nerves. 

spt.IX,  ramus  supratemporalis  IX. 

spt  X,  ramus  supratemporalis  X. 

to  br.pl,  to  brachial  plexus. 


trap,  nerve  to  trapezius  muscle. 
tr.hmd.VII,  truncus  hyomandibularis  VII. 
tr.io.  V  +  VII,   truncus   infra-orbitalis  V  + 

tr.so.  V+VII,  truncus  supra-orbitalis  V  + 

VI,  nervus  abducens. 

VIII,  nervus  acusticus. 

VII  r.ll,  lateral  line  roots  of  facialis. 

visc.X,  ramus  visceralis  (intestinalis)  X. 

vpo,  nerve  to  ventral  pit  organs. 

X  r,  roots  of  vagus. 


tJhe  °UtU"es  °,f  th\nfe,  eye,  spiracle  and  the  five  gill  clefts  are  indicated  by 
the  conventional  symbols  printed  above  the  figure. 

25 


FIG.  5B. 


26 


DISSECTION    OF   THJU   SHARK  27 

Draw  the  contents  of  the  orbit  as  seen  from  above,  including 
the  eye,  its  muscles,  and  all  nerves  which  enter  the  orbit. 

13.  The  eyeball. — Remove  the  eyeball  from  the  orbit  by  cut- 
ting all  of  its  attachments,  and  dissect  the  eye.  Open  the  eye- 
ball by  a  cut  around  the  equator  between  the  cornea  and  the 
optic  nerve.  In  the  inner  half  of  the  eyeball  note  the  three 
coats — the  tough  sclerotic,  the  pigmented  choroid,  and  the 
grayish- white  retina.  The  retina  in  preserved  specimens  is  apt 
to  be  partly  disintegrated  and  pulled  loose  from  the  choroid 
coat.  In  the  outer  half  notice  the  lens  and  observe  its  attach- 
ment by  a  delicate  suspensory  ligament  attached  to  the  margin 
of  the  eyeball  in  front  of  the  retina  The  space  behind  the  lens 
is  filled  with  vitreous  humor  (corpus  vitreum) ;  the  space  in 

FIG.  5B. — An  analysis  of  the  cranial  ganglia  of  Squalus  acanthias  ("pup" 
stage).  The  somatic  motor  roots  are  omitted;  cf.  Fig.  5 A.  For  the  sig- 
nificance of  the  conventional  symbols  see  the  accompanying  legend. 

ABBREVIATIONS 

ac-lat.,  area  acustico-lateralis  of  brain. 

buc.  VII,  ramus  buccalis  VII. 

cbl.,  cerebellum. 

dors.X,  rarnus  dorsalis  X. 

g  ac.,  ganglion  acusticum. 

g  buc.,  ganglion  of  ramus  buccalis  VII. 

gen.,  ganglion  geniculi  VII. 

gg.,  ganglion  gasseri. 

g  gl.,  visceral  ganglion  of  IX. 

g  II.  X,  ganglion  of  rarnus  lateralis  X. 

g  mde.,  lateralis  ganglion  on  hyornandibular  trunk. 

g  op.,  ganglion  of  ramus  ophthalmicus  profundus. 

g  os.  VII,  ganglion  of  ramus  ophthalmicus  superficialis  VII. 

g  spt.IX,  ganglion  of  ramus  supratemporalis  IX. 

g  spt.X,  ganglion  of  ramus  supratemporalis  X. 

g  X.I  to  g  XA,  visceral  sensory  ganglia  on  the  vagus. 

hy.VII,  ramus  hyoideus  VII. 

IX,  nervus  glossopharyngeus. 

IX  r.,  roots  of  nervus  glossopharyngeus. 
lat.X,  ramus  lateralis  X. 

max.  V,  ramus  maxillaris  V. 

md.  V,  ramus  mandibularis  V. 

mde.VlI,  ramus  mandibularis  externus  VII. 

mdi.VII,  ramus  mandibularis  internus  VII. 

mes.,  midbrain. 

op.  V,  ramus  ophthalmicus  profundus  V. 

os.V,  ramus  ophthalmicus  superficialis  V. 

os.  VII,  ramus  ophthalmicus  superficialis  VII. 

pal.VII,  ramus  palatinus  VII. 

rest  b.,  "corpus  restiforme"  (anterior  end  of  acustico-lateral  area). 

spt.IX,  ramus  supratemporalis  IX. 

spt.X,  ramus  supratemporalis  X. 

VII  r.,  roots  of  facialis  proper. 

VII  r  II.,  lateral  line  roots  of  facialis. 

X  r.,  roots  of  vagus  proper. 

X  r  II.,  lateral  line  root  of  vagus. 

X.I  to  XA,  first  to  fourth  branchial  rami  of  vagus. 


28  LABORATORY   OUTLINE    OF   NEUROLOGY 

front  of  the  lens  and  behind  the  cornea  is  filled  with  aqueous 
humor.  The  choroid  coat  is  extended  in  front  of  the  lens  to 
form  the  iris. 

14.  Look  up  the  structure  of  the  human  eye  (see  Section 
135)  and  compare  with  that  of  the  dogfish.  Note  the  dif- 
ference in  the  shape  of  the  lens  in  the  two  cases.  In  mammals 
the  suspensory  ligament  is  attached  to  a  muscular  ridge,  the 
ciliary  process,  whose  ciliary  muscles  control  the  accom- 
modation of  the  lens.  In  the  dogfish  the  ciliary  muscles 
are  feebly  developed  and  there  is  little,  if  any,  power  of 
accommodation. 

The  anatomy  of  the  mammalian  eye  should  be  studied 
in  formalin  hardened  and  fresh  specimens.  The  ox  eye  is 
the  most  satisfactory,  but  that  of  the  sheep  or  pig  may 
be  used.  Begin  the  study  of  the  general  relations  of  the 
parts  using  a  hardened  eyeball  cut  through  the  optic  axis. 
Identify:  cornea,  iris,  lens,  ciliary  body,  retina,  chorioidea, 
sclera.  If  fresh  material  is  not  available,  study  the  anterior 
and  posterior  segments  of  the  eyeball  cut  transverse  to  the 
optic  axis  just  anterior  to  the  equator.  See:  Cunningham 
('15),  pp.  806-827;  Gray  ('18),  pp.  1000-1029;  Morris  ('14), 
pp.  1051-1081;  Piersol  ('16),  pp.  1436-1483;  Quain  ('09), 
Vol.  Ill,  Pt.  II,  pp.  173-264;  Rauber-Kopsch  ('12),  Abteilung 
VI,  pp.  97-170;  Sobotta  ('11),  pp.  247-274;  Spalteholz  ('09), 
pp.  770-798;  Toldt  ('04),  pp.  892-910. 

If  fresh  material  is  available,  determine,  if  possible,  whether 
you  have  right  or  left  eye  by  identifying  the  eyelids,  the 
rudiment  of  the  nictitating  membrane  (plica  semilunaris),  the 
papillae  lacrimales,  the  naso-lachrimal  duct,  the  ocular 
muscles,  and  the  point  of  entrance  of  the  optic  nerve.  In 
the  ox  the  compact  group  of  muscles  around  the  optic  nerve 
inserted  into  the  posterior  hemisphere  of  the  eyeball  is  the 
m.  retractor  bulbi  which  is  not  present  in  man. 

Remove  the  conjunctiva  and  the  capsule  of  Tenon  (fascia 
bulbi)  by  making  a  circular  incision  around  the  eyeball 
just  behind  the  sulcus  sclerae,  carrying  it  as  far  as  the  sclera 
only  and  stripping  forward  and  backward  to  the  optic  nerve. 
Look  for  the  trunks  of  the  venae  vorticosae  emerging  from  the 
sclera  and  the  long  and  short  ciliary  nerves  (Sobotta,  '11, 


DISSECTION    OF   THE    SHARK  29 

Fig.  731).  Now  snip  through  the  sclera  near  the  equator 
being  careful  not  to  injure  the  dark  chorioid  tunic.  Then 
put  the  specimen  into  water  and;  separating  the  sclera  and 
chorioidea,  remove  the  former,  at  least  in  part.  Brushing 
away  the  pigment  will  serve  to  demonstrate  the  venae  vorti- 
cosse.  Look  for  the  ciliary  nerves.  Identify  the  region  of 
the  ciliary  body  and,  cutting  away  the  cornea,  expose  the 
iris. 

The  anterior  and  posterior  hemispheres  may  now  be 
separated  by  cutting  through  the  chorioidea  and  retina  and 
loosening  the  corpus  vitreum  from  the  ciliary  region.  Study 
the  anterior  segment  with  a  hand  lense  and  identify:  retina, 
ora  serrata,  orbicularis  ciliaris,  processus  ciliaris  and  iris. 
By  an  incision  into  the  capsule  of  the  lens  remove  the  latter 
and  note  its  shape  and  consistency.  See:  Cunningham  ('15), 
Fig.  686;  Morris  ('14),  Fig.  801;  Sobotta  ('11),  Figs.  733-736; 
Spalteholz  ('09),  Fig.  840.  In  the  posterior  segment  identify 
the  papilla  optica  (blind  spot)  and  retinal  vessels.  When  the 
retina  is  stripped  off,  the  pigment  layer  usually  remains 
adherent  to  the  chorioid.  It  is  partly  replaced  in  the  ox  by 
the  iridescent  tapetum. 

If  microscopic  sections  are  available  study  the  structure 
about  the  iridial  angle  and  the  layers  of  the  retina.  For 
details  of  structure  of  the  retina  see  Section  135. 

15.  Cranial  Nerves. — 'There  are  ten  pairs  of  cranial  nerves 
(the  XI  and  XII  human  nerves  are  not  separately  represented) . 
The  spinal  nerves  are  much  alike,  each  pair  repeating  the  same 
functional  pattern;  but  no  two  cranial  nerves  have  the  same 
functional  composition.  Accordingly,  in  studying  the  cranial 
nerves  it  is  necessary  to  determine  for  each  pair  of  nerves  the 
functional  composition  of  each  of  its  roots  and  the  precise  periph- 
eral and  central  connections  of  the  fibers  of  each  functionally 
distinct  root.  This  has  been  done  for  a  sufficient  number  of 
vertebrate  types  to  establish  a  typical  vertebrate  pattern  of 
cranial  nerve  components.  These  functionally  defined  com- 
ponents are  classified  in  four  major  groups,  somatic  sensory  and 
motor  and  visceral  sensory  and  motor,  each  of  which  may  be 
further  subdivided.  For  the  discussion  of  the  principles  and 
mode  of  application  of  this  classification  (which  is  fundamental 


30  LABORATORY    OUTLINE    OF   NEUROLOGY 

to  an  understanding  of  the  following  sections),  see  Herrick,  '18, 
Chap.  IX,  and  Johnston  ('06),  Chap.  V. 

16.  The  nerve  components  of  the  dogfish  have  been  carefully 
studied  microscopically  by  Dr.  H.  W.  Norris  and  Miss  S.  P. 
Hughes,  who  have  very  kindly  prepared  for  us  the  accompany- 
ing drawings    Figs.  4  and  5)  from  a  detailed  account  to  be 
published  shortly  ('19).     The  systems  of  nerve  components 
mentioned  at  the  close  of  the  preceding  section  are  represented 
in  the  following  cranial  nerves  of  the  dogfish : 

(1)  Somatic  sensory:  II  (optic);  III,  IV  and  VI  (fibers  of 
muscle  sense);  V  (general  cutaneous  and  muscle  sense);  VII 
(lateral  line  fibers) ;  VIII  (acoustic  and  vestibular) ;  IX  (lateral 
line  fibers);  X  (lateral  line  fibers). 

(2)  Somatic  motor:  III,  IV  and  VI  (eye-muscle  nerves)  [in 
man  also  XII,  for  tongue  muscles,  represented  in  the  dogfish  by 
the  hypobranchial  nerve  (Fig.  5 A)]. 

(3)  Visceral  sensory:  I  (olfactory);  VII,  IX  and  X  (general 
visceral  and  gustatory  nerves). 

(4)  Visceral  motor:  III    (ciliary   nerves);   V    (masticatory 
nerves) ;  VII .  (nerves  of  the  hyoid  musculature  [including  in 
man  the  facial  muscles]);  IX  and  X  (branchial  and  general 
visceral  motor  nerves). 

17.  The  names  of  the  cranial  nerves  and  their  chief  branches 
in  the  dogfish  are  given  for  reference  in  the  following  list  (cf. 
Figs.  1  to  5).     They  should  be  identified  in  your  specimens,  but 
their  names  need  not  be  memorized.     The  human  canial  nerves 
show  the  same  general  arrangement,  save  for  the  absence  in 
man  of  all  components  supplying  lateral  line  organs  and  for 
the  modification  of  the  IX  and  X  pairs  resulting  from  the  loss 
of  the  gills.     See  Section  47. 

I.  N.  olfactorius.     Passes  in  very  numerous  short  filaments 
from  the  nasal  sac  on  the  ventral  surface  of  the  snout  to  the 
very  large  olfactory  bulb.     Associated  with  this  nerve  is  the 
slender  nervus  terminalis,  running  between  the  nasal  sac  and 
the  cerebral  hemisphere  (Figs.  2  and  5 A).     It  passes  along  the 
dorsal  surface  of  the  olfactory  bulb  and  the  medial  surface  of 
the  stalk  of  the  bulb  to  enter  the  cerebral  hemisphere  near  the 
median  plane.     See  Locy  ('05)  and  McKibben  ('14). 

II.  N.  opticus.     From  the  eye  to  the  floor  of  the  brain  under 
the  thalamus. 


DISSECTION    OF    THE    SHARK  31 

III.  N.   oculomotorius.     From  the  floor  of  the  midbrain 
to  mm.   obliquus  inferior   and   rectus  superior,  inferior,  and 
medialis. 

IV.  N.  trochlearis.     From  the  roof  of  the  midbrain  to  m. 
obliquus  superior. 

VI.  N.  abducens.  From  the  floor  of  the  medulla  oblongata 
to  m.  rectus  lateralis. 

V  and  VII.  The  trigeminus  and  facialis  nerves  are  so  inti- 
mately united  that  microscopic  methods  are  required  for  their 
separation.  In  Figs.  2  and  3  they  are  drawn  very  diagram- 
matically  after  slight  dissection  and  separation  of  the  roots  and 
ganglia.  Their  true  composition  is  shown  in  Fig.  5.  The  two 
upper  (more  rostral)  roots  of  the  complex  are  the  sensory  and 
motor  V;  the  lower  ones  belong  to  VII.  The  sensory  V  root 
receives  its  fibers  from  the  skin  of  the  whole  head  in  front  of 
the  gill  region.  The  motor  V  root  supplies  the  jaw  muscles; 
the  motor  VII  root  those  of  the  hyoid  arch.  The  sensory  VII 
root  (nervus  intermedius,  or  portio  intermedia  of  Wrisberg) 
receives  most  of  its  fibers  from  taste-buds  and  the  mucous 
lining  of  the  mouth.  The  lateral  line  roots  which  enter  the 
brain  in  front  of  the  ear  are  usually  named  as  parts  of  the  VII 
nerve;  see  Section  18. 

VIII.  N.  acusticus.     From  the  labyrinth  of  the  ear  to  the 
acoustico-lateral  area  of  the  medulla  oblongata.     The  cochlear 
ramus  is  absent  or  rudimentary.     A  small  sensory  spot  in  the 
saccule,  the  lagena,  is  regarded  as  the  organ  from  which  the 
cochlear  sense  organ  (spiral  organ)  of  mammals  has  been  differ- 
entiated;   its    nerve,    accordingly,  •  is    homologous    with    the 
cochlear  nerve  of  man. 

IX.  N.  glossopharyngeus.     Arises  from  the  oblongata  by 
three  roots,  two  sensory  and  one  motor,  passes  under  the  mem- 
branous labyrinth  of  the  ear  and  forks  around  the  first  gill  cleft. 
It  contains  visceral  sensory  and  visceral  motor  fibers  for  the 
innervation  of  the  first  gill  and  also  a  small  lateral  line  com- 
ponent (r.  supratemporalis  IX,  Figs.  4  and  5). 

X.  N.  vagus.     Arises  from  the  oblongata  by  several  roots 
which  form  a  large  trunk  from  which  arise  branchial  rami  to 
fork  around  the  second  to  fifth  gill  clefts  (visceral  motor  and 
visceral  sensory);  also  r.  visceralis  vagi  for  the  viscera  of  the 


32  LABORATORY    OUTLINE    OP    NEUROLOGY 

body  cavity  farther  back  (esophagus,  stomach,  etc.).  The  r. 
dorsalis  vagi  contains  lateral  line  fibers  for  part  of  the  main 
lateral  canal.  The  r.  lateralis  vagi  supplies  the  lateral  canal 
behind  the  region  reached  by  the  r.  dorsalis.  The  r.  supra- 
temporalis  vagi  supplies  the  anterior  end  of  the  lateral  canal 
and  the  supratemporal  canal.  All  lateral  line  fibers  of  the 
vagus  arise  by  a  large  root  farther  forward  (rostral)  than  the 
other  vagus  roots. 

The  human  accessory  nerve  (XI)  is  represented  by  a  branch 
of  the  vagus  (Fig.  5A,  trap.)  and  the  hypoglossus  (XII)  by  fibers 
of  the  occipital  nerves  which  enter  the  hypobranchial  nerve. 

18.  The  acoustico-lateral  complex.  The  membranous  laby- 
rinth and  the  lateral  line  organs  comprise  a  complex  system  of 
sense  organs  with  many  features  in  common  (see  Johnston 
('06),  Chap.  VII  and  S.  E.  Johnson  ('17)).  Within  the  lateral 
line  canals  and  ampullae  of  Lorenzini  are  found  sense  organs 
which  resemble  those  of  the  internal  ear,  and  the  nerves  which 
supply  them  enter  the  same  part  of  the  brain,  the  area  acustico- 
lateralis  (see  Section  22  and  Figs.  2  to  5).  The  sense  organs 
of  the  saccule  in  fishes  are  sensitive  to  sound  waves;  those  of 
the  ampullae  of  the  semicircular  canals  assist  in  maintaining 
equilibrium;  and  those  of  the  lateral  line  organs  are  sensitive 
to  water  vibrations  of  a  slower  rate  than  the  sound  wavef  re- 
ceived by  the  ears,  with  possibly  other  functions  in  addition. 

The  nerves  terminating  in  the  area  acustico-lateralis  consti- 
tute a  functional  and  anatomical  system  distinct  from  all  other 
sensory  nerves,  though  peripherally  they  may  be  bound  up  in 
the  same  nerve-trunks  with  other  components.  They  are 
most  closely  related  with  the  general  cutaneous  nerves.  They 
reach  their  peripheral  end-organs  through  the  following  nerve 
trunks  (cf .  the  next  section) : 

(1)  For  the  supra-orbital  canal  from  the  supra-orbital  trunk 
(this  component  of  this  trunk  is  called  the  ramus  ophthalmicus 
superficialis  VII). 

(2)  For  the  infra-orbital  canal  from  the  infra-orbital  trunk 
(this  component  is  called  the  ramus  buccalis  VII). 

(3)  For  the  hyomandibular  canal  from  the  facial  trunk  or 
hyomandibular  nerve  (called  the  ramus  mandibularis  externus 
VII). 


DISSECTION    OF   THE    SHARK  33 

(4)  For  the  internal  ear  from  the  nervus  acusticus. 

(5)  For  the  lateral  line  organs  of  the  temporal  canal  from 
the  ramus  supratemporalis  IX. 

(6)  For  the  lateral  line  canal  of  the  body  from  the  ramus 
supratemporalis,  ramus  dorsalis,  and  ramus  lateralis  X. 

The  nerve-fibers  of  this  system  which  supply  the  irregularly 
arranged  ampullae  of  the  head  distribute  in  company  with  those 
for  the  lateral  line  canals  of  the  head. 

19.  Many  of  the  peripheral  nerve-trunks  are  mixed  in  the  sense 
that  they  contain  functionally  different  components.  These 
components  may  come  from  roots  of  several  different  nerves  by 
anastomoses  peripherally  of  the  ganglia.  Some  of  the  more 
important  peripheral  nerves  of  the  dogfish  are  as  follows: 

(1)  The  supra-orbital  trunk,  containing  the  r.  ophthalmicus 
superficialis  V  (general  cutaneous)  for  the  skin  of  the  top  of  the 
head,  and  lateral  line  fibers  for  supra-orbital  lateral  line  organs 
(the  r.  ophthalmicus  superficialis  VII);  (2)  r.  ophthalmicus 
profundus  V  (general  cutaneous),  passing  through  the  middle 
of  the  orbit,  beyond  which  it  anastomoses  with  the  r.  ophthal- 
micus superficialis  V  to  supply  the  skin  of  the  snout  (the 
superficial  and  deep  ophthalmic  branches  of  the  V  nerve  to- 
gether correspond  approximately  with  the  ophthalmic  branch 
of  the  human  trigeminus) ;  (3)  the  infra-orbital  trunk,  passing 
across  the  floor  of  the  orbit,  below  which  it  divides  into  the  r. 
buccalis  VII  (lateralis)  for  infra-orbital  lateral  line  organs,  r. 
maxillaris  V  (general  cutaneous)  for  the  skin  of  the  upper  jaw, 
and  r.  mandibularis  V  (general  cutaneous  and  motor)  for  the 
skin  and  muscles  of  the  lower  jaw;  (4)  r.  palatinus  VII  (visceral 
sensory)  for  the  mucous  membrane  and  taste-buds  of  the  roof 
of  the  mouth  (represented  by  the  great  superficial  petrosal 
nerve  of  the  human  body) ;  (5)  the  hyomandibular  trunk,  pass- 
ing behind  the  spiracular  cleft  to  the  region  of  the  hyoid  arch 
and  lower  jaw,  containing  the  r.  mandibularis  internus  VII 
(visceral  sensory)  for  taste-buds  and  mucous  membrane  lining 
the  lower  jaw,  motor  VII  fibers  for  muscles  of  the  hyoid  arch 
(r.  hyoideus),  and  lateral  line  fibers  for  hyomandibular  lateral 
line  organs  (r.  mandibularis  externus  VII).  The  visceral 
sensory  and  motor  fibers  correspond  with  the  facial  trunk  of 
the  human  body. 


34  LABORATOKY   OUTLINE    OP   NEUROLOGY 

The  components  of  these  peripheral  nerves  can  be  com- 
pletely separated  only  by  microscopic  methods,  though  a  skil- 
ful dissector  can  separate  the  lateralis  components  of  many  of 
the  nerves  (see  Ewart,  '93  and  Norris  and  Hughes,  '19).  The 
nerve  components  of  vertebrates  are  fully  described  by 
Johnston  ('06  and  '09). 

20.  The  gills  are  visceral  structures.     Their  sensory  nerves 
terminate  centrally  in  the  visceral  sensory  column  of  the 
medulla  oblongata,  and  their  motor  nerves  arise  from  the 
visceral  motor  column  (see  Sections  15  and  23).     Each  gill  cleft 
has  a  branchial  nerve,  as  illustrated  in  Figs.  1,  2,  5A,  and  6. 
The  branchial  trunk  typically  divides  into:  (1)  a  postbranchial 
(or    posttrematic)    nerve,    containing    visceral   sensory   and 
visceral  motor  components,  (2)  a  prebranchial  (or  pretrematic) 
nerve    (visceral  sensory),    (3)    a  pharyngeal  nerve    (visceral 
sensory).     The   postbranchial  division  of  the   IX  nerve   of 
fishes  is  homologous   with   the  human  lingual  branch,   for 
distribution  to  the  tongue. 

The  roots  of  the  IX  nerve  connect  with  the  medulla  oblon- 
gata a  short  distance  behind  the  VIII  nerve,  and  the  IX  nerve 
itself  can  be  seen,  after  the  dissection  of  the  internal  ear,  run- 
ning across  the  floor  of  the  auditory  chamber.  Dissect  the  IX 
nerve  outward  and  note  its  division  into  prebranchial  and  post- 
branchial  rami. 

The  roots  of  the  X  nerve  arise  behind  those  of  the  IX  (except 
the  lateral  line  root  which  arises  farther  forward  from  the 
acoustico-lateral  area) .  Dissect  the  vagus  trunk  outward  and 
note  its  division  into  lateralis  and  branchial  trunks.  The 
latter,  after  giving  off  the  branchial  rami  to  the  second  to  fifth 
gills,  is  continued  backward  to  form  the  ramus  intestinalis 
and  ramus  cardiacus. 

21.  The  student  should  at  this  time  acquire  a  general  famili- 
arity with  the  arrangement  of  the  human  spinal  and  cranial 
nerves.     The  cranial  nerves  of  the  dogfish  are  broadly  similar 
to  the  corresponding  nerves  in  the  human  body.     Some  of  the 
more  important  differences  are  as  follows:  the  absence  in  the 
dogfish  of  the  XI  and  XII  pairs  and  of  the  cochlear  branch  of 
the  VIII  pair  (the  rudiments  of  these  nerves  are  present- 
see  Section  17);  the  presence  in  the  dogfish  of  functional  gills 


DISSECTION   OP  THE   SHAKE  35 

with  corresponding  modifications  of  the  IX  and  X  pairs  of 
nerves;  the  presence  in  the  dogfish  of  an  extensive  special 
system  of  subcutaneous  sense  organs  structurally  (and  prob- 
ably physiologically)  related  to  those  of  the  internal  ear. 
These  are  the  sense  organs  of  the  lateral  line  canals  and 
ampullae  of  Lorenzini,  for  which  there  is  a  special  system  of 
nerves,  the  lateralis  components  of  the  VII,  IX,  and  X  nerves 
(see  Section  18). 

Draw  the  dissection  of  the  brain  and  cranial  nerves,  indi- 
cating the  functional  components  in  each  peripheral  nerve- 
trunk  by  colors  in  accordance  with  the  scheme  given  in  Section 
62  (p.  62),  coloring  the  lateral  line  nerves  the  same  as  the  VIII 
nerve  (brown  or  green). 

22.  Complete  the  exposure  of  the  brain,  carefully  preserving 
the  roots  of  the  cranial  nerves. 

Now,  viewing  the  brain  from  above,  review  the  arrangement 
and  physiological  composition  of  the  cranial  nerves  and  note 
particularly  the  part  of  the  brain  with  which  each  peripheral 
end-organ  or  group  of  physiologically  similar  organs  is  related. 
Simple  inspection  shows  that  the  organs  of  smell  are  connected 
with  the  olfactory  bulbs,  and  in  fact  these  and  almost  the 
whole  of  the  cerebral  hemispheres  and  epithalamus  and  hypo- 
thalamus  form  the  olfactory  part  of  the  brain  (stippled  in  Figs. 
2  and  3) .  In  the  same  way  the  eyes  are  related  with  the  optic 
lobes  of  the  midbrain  (obliquely  cross-hatched  in  Figs.  2  and  3), 
the  ears  and  lateral  line  organs  with  the  acoustico-lateral  area 
(cross-hatched  with  horizontal  lines),  and  the  nerves  of  general 
skin  sensibility  with  the  general  cutaneous  area  (unshaded). 
Locate  precisely  these  areas  on  your  specimen. 

23.  Next  carefully  remove  the  membranous  roof  of  the 
fourth  ventricle  and  study  the  floor  of  the  fourth  ventricle, 
noting  the  following  structures,  passing  from  the  median  sulcus 
laterally  (cf .  Figs.  2  and  6) :  (1)  a  longitudinal  ridge  marking 
the  position  of  the  fasciculus  longitudinalis  medialis  ("  pos- 
terior longitudinal  fasciculus")  and  farther  ventrally  the  posi- 
tion of  the  ventral  gray  column  of  the  spinal  cord  and  nuclei 
of  the  VI,  IV,  and  III  cranial  nerves — this  is  the  somatic  motor 
column;  (2)  a  wide  longitudinal  groove  parallel  with  the  last, 
below  which  are  found  the  motor  nuclei  of  the  X,  IX,  VII, 


36  LABORATORY   OUTLINE    OF   NEUROLOGY 

and  V  cranial  nerves — this  is  the  visceral  motor  column  and  is 
the  forward  extension  of  the  lateral  gray  column  of  the  spinal 
cord;  (3)  a  longitudinal  ridge  with  a  beaded  contour,  which 
contains  the  terminal  centers  of  the  visceral  sensory  com- 
ponents of  the  X,  IX,  and  VII  cranial  nerves — the  vi  ceral 
sensory  column;  (4)  separated  from  the  last  by  a  deep  groove 
and  forming  the  dorso-lateral  wall  of  the  fourth  ventricle  is 
the  somatic  sensory  column.  This  column  is  the  continuation 
of  the  dorsal  gray  column  of  the  spinal  cord,  and  its  ventral 
part  contains  the  centers  for  the  general  cutaneous  nerves  of 
the  trunk  and  head.  The  dorsal  part  of  this  column  is  the 
area  acustico-lateralis,  whose  anterior  end  is  greatly  enlarged 
under  the  cerebellum,  with  which  it  is  directly  continuous. 
This  area  receives  the  VIII  and  lateral  line  nerves,  and  the 
cerebellum  is  a  specialized  derivative  of  it.  The  longitudinal 
groove  between  columns  2  and  3  is  the  sulcus  limitans  (cf .  the 
development  of  the  human  brain,  Section  38).  It  separates 
motor  centers  below  (ventrally)  from  sensory  centers  lying 
farther  dorsally. 

24.  From  these    observations    it  appears  that  the  brain 
shows  various  external  thickenings  or  enlargements,  each  of 
which  is  related  to  a  particular  physiological  type  of  end- 
organ.     We    may,  in   fact,  recognize  a  "nose  brain,"  "eye 
brain/'  "ear  brain,"  etc.,   and  in   addition   the   cerebellum 
above    these    primary   sensorimotor   centers.     There   is   no 
cerebral  cortex. 

25.  Draw  the  medulla  oblongata  from  the  dorsal  side,  twice 
natural  size,  after  removal  of  the  membranous  roof ,  to  illustrate 
the  functional  areas  in  the  walls  of  the  fourth  ventricle.     In 
this  drawing  the  functional  columns  should  be  tinted  to  cor- 
respond with  the  colors  used  in  the  drawing  of  the  peripheral 
nerves  (Section  21).     Thus,  the  acoustico-lateral  area  will  be 
colored  the  same  as  the  VIII  and  lateral  line  nerves,  the  gen- 
eral somatic  sensory  area  the  same  as  the  general  cutaneous 
nerves,  etc.     The  drawing  of  the  entire  brain  called  for  in 
Section  21  may  also  be  tinted  in  the  same  way. 

26.  The  physiologically  distinct  areas  noted  in  the  preceding 
sections  tend  to  be  grouped  in  larger  regions,  the  pattern  of  this 
grouping  being  determined  in  part  by  the  primitive  segmenta- 


DISSECTION   OF  THE   SHARK  37 

tion  and  development  of  the  brain  and  in  part  by  physiological 
convenience. 

The  brain  is  separated  by  a  constriction  (the  isthmus)  in 
front  of  the  cerebellum  into  the  cerebrum  in  front  and  the 
rhombic  brain  (rhombencephalon)  below,  the  latter  being 
further  subdivided  into  the  medulla  oblongata  and  cerebellum. 
The  cerebrum  is  further  subdivided  into  (1)  the  midbrain 
(mesencephalon)  containing  the  optic  lobes  dorsally  and  the 
cerebral  peduncles  and  motor  centers  for  eye  movements 
ventrally,  (2)  the  between-brain  (diencephalon)  containing 
thalamus,  epithalamus,  and  hypothalamus,  and  (3)  the  end- 

fourth  ventricle >^_T2T^'\^ -somatic  sensory 

column 
-visceral  sensory 

branchial  ganglion.  \^^&-^J :;-::-J         column 

'-visceral  motor 
column 


pharyngeal  nerve^^f/^         \_      J^_^><^  somatic  motor 

.....  column 

pre-branchial 


FIG.  6.  —  Diagrammatic  cross-section  through  the  medulla  oblongata  of 
the  dogfish  in  the  region  of  the  vagus  nerve  to  illustrate  the  innervation 
of  the  gills  and  the  arrangement  of  the  functional  columns  of  the  oblongata. 
The  groove  between  the  visceral  motor  column  and  the  visceral  sensory 
column  is  the  sulcus  limitans. 

brain  (telencephalon)  comprising  the  anterior  end  of  the  brain 
tube,  the  cerebral  hemispheres,  and  olfactory  bulbs.  Locate 
these  regions  and  compare  the  fuller  study  of  the  subdivisions 
and  development  of  the  brain  in  Section  40. 

27.  Now  remove  the  brain  from  the  cranial  cavity,  first  care- 
fully cutting  the  nerve-roots  so  as  to  permit  their  subsequent 
identification  and"  avoiding  injury  to  the  olfactory  bulbs  in 
front  and  the  pituitary  body  on  the  ventral  surface.     Examine 
the  ventral  surface  and  complete  the  study  of  the  parts  listed 
in  Section  26. 

28.  Make  a  transverse  section  across  the  medulla  oblongata 
at  the  level  of  the  roots  of  the  VIII  nerves.     Compare  this  sec- 
tion with  a  similar  one  made  in  the  vagus  region  (Fig.  6)  and 
note  the  differences. 


38  LABORATORY    OUTLINE    OF   NEUROLOGY 

Draw  the  transverse  section  at  the  level  of  the  VIII  nerves 
and  designate  on  it  the  structures  in  the  walls  of  the  fourth 
ventricle  enumerated  in  Section  23. 

29.  Now  divide  the  entire  brain  into  two  lateral  halves  by  a 
vertical  median  cut  and  study  the  course  of  the  ventricles  as 
thus  exposed,  noting  the  narrowing  of  the  fourth  ventricle  into 
the  aqueduct  of  Sylvius  in  the  isthmus,  its  lateral  expansion  in 
the  optic  lobes  (optocele),  the  vertical  expansion  in  the  thalamus 
(third  ventricle),  and  the  connection  of  the  latter  with  the  first 
and  second  ventricles  in  the  cerebral  hemispheres  through  the 
foramen  of  Monro  (foramen  interventriculare)  on  each  side. 


IV.  THE  MAMMALIAN  NERVOUS  SYSTEM 
i.  Introductory  Topics 

30.  The  directions  which  follow  can  be  applied  to  any  of  the 
larger  mammalian  brains.  If  human  brains  are  available  in 
sufficient  numbers,  these  alone  may  be  used;  but  in  case  the 
available  human  brains  are  insufficient  in  number  or  poorly 
preserved,  the  gross  dissections  may  be  made  on  brains  of  the 
sheep,  dog,  or  cat.  The  brain  of  the  sheep  is  advised.  Heads 
of  freshly  killed  lambs  can  usually  be  procured  from  the 
butchers.  As  soon  as  possible  after  the  killing  the  brain  should 
be  removed  and  hardened  for  a  few  days  before  use  by  immers- 
ing it  in  a  10  per  cent,  solution  of  commercial  formalin  in  water. 
In  this  solution  it  may  be  preserved  indefinitely. 

To  remove  the  brain,  first  loosen  the  top  of  the  skull  with  a 
saw  and  chisel.  Hold  the  head  firmly  in  a  vise  dorsal  side  up. 
First  with  a  saw  make  a  transverse  cut  from  5  to  10  mm.  deep 
across  the  top  of  the  head  about  1  cm.  behind  the  anterior 
borders  of  the  bony  orbits.  Then  along  each  side  of  the  head 
make  an  obliquely  longitudinal  saw  cut,  beginning  just  above 
the  occipital  condyles  and  extending  forward  across  the 
dorsal  surface  of  the  head  about  2  cm.  medial  to  the  inner 
border  of  the  bony  orbit.  The  lines  of  these  two  cuts  should 
follow  the  curvature  of  the  head  and  meet  in  the  middorsal 
plane  about  2  cm.  in  front  of  the  transverse  cut  already 
made  and  the  saw  should  be  inclined  about  45  degrees  down- 
ward and  inward.  Avoid  cutting  so  deeply  as  to  enter  the 
brain  substance.  Then  make  a  very  shallow  transverse  cut 
through  the  cranium  immediately  above  the  occipital  condyles. 
With  chisel  and  mallet  clip  through  the  occipital  condyles  be- 
hind the  cut  last  made,  and  also  break  the  remaining  bridge  of 
bone  medially  of  each  bony  orbit.  The  top  of  the  cranium 
may  now  be  pried  loose  with  the  chisel  and  lifted  off.  The  dura 
mater  should  be  cut  around  with  scissors  along  the  line  of  the 
cut  surface  of  the  skull  and  the  ventral  part  of  the  dura  left 
attached  to  the  skull  floor.  Lift  up  the  brain  from  the  cranial 

39 


40  LABORATORY    OUTLINE    OF   NEUROLOGY 

floor  and  cut  the  nerve-roots  with  a  slender  scalpel  or  scissors. 
Carefully  free  the  anterior  and  ventral  surfaces  of  the  olfactory 
bulb  from  the  lamina  cribrosa  of  the  ethmoid  bone,  cutting  off 
the  filaments  of  the  olfactory  nerve.  Cut  out  the  hypophysis 
from  its  cranial  pocket  in  the  sella  turcica  and  leave  it  attached 
to  the  brain  by  the  slender  infundibulum.  The  brain  may  now 
be  lifted  out  of  the  cranial  cavity  and  preserved  in  formalin. 

31.  As  stated  above,  most  of  the  dissections  described  in  this 
Outline  can  be  made  on  either  human  or  other  brains.     If  brains 
of  the  sheep  (or  dog  or  cat)  are  used,  specimens  and  text-book 
figures  of  the  human  brain  should  be  kept  constantly  at  hand 
for  comparison.     A  certain  number  of  special  dissections  illus- 
trating particular  features  should  be  made  in  advance  and  pre- 
served permanently.     These  should  -be  made,  if  possible,  on 
human  brains  and  should  include,  among  others,  three  brains 
sliced   respectively  in   planes   parallel   with   the   transverse, 
frontal,  and  sagittal  planes  of  the  body.     Valuable  demonstra- 
tion specimens  may  also  be  made  by  following  out  the  direc- 
tions for  dissecting  the  several  fiber  systems  given  in  the 
"optional  dissections"  (Sections  102-111  and  141-152),  using 
a  separate  brain  or  half  brain  for  each  system.     Cunningham 
and  Waterson's  Edinburgh  University  Stereoscopic  Atlas  is 
a  valuable  aid  in  getting  true  pictures  of  the  internal  structures. 

If  only  one  human  brain  is  available  for  study,  it  is  advised 
that  it  be  dissected  as  directed  by  Dr.  Lineback  ('15).  By  this 
procedure  the  brain  is  first  divided  in  the  median  plane  into 
right  and  left  halves  and  one  of  these  halves  is  then  further 
dissected  by  a  single  carefully  planned  incision  so  as  to  remove 
a  considerable  portion  of  the  cerebral  hemisphere  from  the 
brain  stem  and  at  the  same  time  reveal  the  internal  structure 
of  the  hemisphere.  The  method  has  the  further  advantage 
that  the  three  parts  into  which  the  brain  is  cut  can  readily  be 
reassembled,  so  that  the  specimen  can  still  be  used  for  demon- 
stration of  the  external  form  in  its  entirety. 

32.  The  dissection  of  many  fiber  tracts  can  be  carried  much 
farther  in  well-preserved  human  brains  than  is  possible  in 
brains  of  lower  animals.     Accordingly,  there  are  included  in 
this  Outline  directions  for  a  certain  number  of  "  optional  dissec- 
tions" (Sections  102-111,  141-152),  for  which  human  brains 


THE   MAMMALIAN   NERVOUS   SYSTEM  41 

well  hardened  in  formalin  are  necessary.  All  of  the  dissections 
here  outlined,  except  a  few  of  the  " optional  dissections"  can  be 
made  on  one  lateral  half  of  a  single  well-preserved  human  brain 
and  all  except  the  " optional  dissections"  can  be  made  on  the 
brain  of  the  sheep,  though  a  better  mastery  of  the  subject  will 
be  obtained  by  following  this  first  dissection  with  a  second 
specimen,  varying  the  procedure  as  may  be  necessary  to  bring 
out  any  special  features  desired.  If  time  and  material  permit, 
it  is  recommended  that  one  specimen  (either  human  or  sheep) 
be  dissected  through  as  directed  and  the  microscopic  prepara- 
tions studied,  and  then,  with  the  aid  of  the  experience  thus 
acquired,  the  more  difficult  " optional  dissections"  may  be 
made  on  a  second  specimen,  the  human  brain  being  used  in  this 
case.  This  Outline  is  prepared  with  this  procedure  in  mind; 
but  it  should  be  repeated  that  the  directions  for  the  use  of  the 
brain  of  the  sheep  can  be  applied  to  the  human  brain  as  well,  if 
this  is  preferred.  A  very  satisfactory  study  of  the  brain  can  be 
made  on  gross  material  alone  if  microscopic  sections  are  not 
at  hand,  though  a  few  such  preparations  illustrating  the  histo- 
logical  elements  are  very  desirable. 

The  practice  at  The  University  of  Chicago,  where  twelve 
weeks  are  allotted  to  the  course  in  neurology,  is  to  provide  each 
student  with  an  entire  sheep's  brain  and  one  lateral  half  of  a 
human  brain  taken  from  a  dissecting-room  cadaver.  Through- 
out the  study  of  the  external  form  of  the  brain  both  specimens 
are  kept  before  the  student  and  every  part  studied  is  identified 
on  both  brains  and  the  differences  noted.  On  this  material  all 
of  the  dissections  here  outlined  can  be  made,  with  the  exception 
of  some  of  the  "  optional  dissections,"  for  which  the  cadaver 
brains  are  usually  not  sufficiently  well  preserved.  A  limited 
number  of  better  preserved  formalin  hardened  human  brains 
are  set  aside  for  the  use  of  any  students  who  can  give  the 
necessary  additional  time  for  the  optional  dissections,  these 
dissections  being  made  in  a  review  course  after  the  completion 
of  the  other  work.  If,  as  just  suggested,  a  second  specimen  of 
the  human  brain  is  dissected,  the  cerebellum  should  not  be 
removed  as  directed  in  Section  49,  thus  permitting  a  more  com- 
plete dissection  of  the  cerebellar  peduncles  (see  Sections 
103-105).  This  specimen,  however,  may  be  divided  in  the 


42  LABORATORY    OUTLINE    OF    NEUROLOGY 

median  plane,  for  the  optional  dissections  are  so  planned  that 
all  of  them  can  be  made  on  one  lateral  half  of  one  brain. 

33.  In  the  interest  of  economy,  both  of  material  and  of  the 
student's  time,  it  is  desirable  that  in  the  first  dissection  the 
order  of  procedure  here  outlined  be  followed  exactly.     In  par- 
ticular, in  the  dissection  of  the  sheep  (or  of  the  human  brain  in 
case  this  is  used  for  the  first  dissection)  where  some  of  the 
dissections  are  to  be  made  on  the  right  side  of  the  brain  and 
some  on  the  left,  the  dissection  must  be  made  on  the  side 
directed  in  order  not  to  interfere  with  later  procedures.     The 
appropriate  portion  of  the  Laboratory  Outline  should  be  read 
and  text-books  consulted  before  each  laboratory  exercise,  and 
a  certain  general  familiarity  with  the  parts  to  be  studied  thus 
secured  in  advance. 

Both  laboratory  and  lecture  work  should  be  daily  supple- 
mented by  careful  study  of  the  text-books  and  atlases.  But  the 
laboratory  notebook  is  primarily  a  record  of  your  own  observa- 
tions. The  notebook  should  always  show  the  source  of  any 
second-hand  matter  introduced  from  text-books  and  other 
authorities  by  way  of  correlation.  Record  the  observations  so 
far  as  possible  by  drawings.  Make  them  neat.  See  that  they 
are  fully  and  neatly  labeled.  When  for  any  reason  the  draw- 
ings specified  do  not  record  fully  or  faithfully  your  observa- 
tions, supplement  them  by  written  notes.  These  must  be 
written  in  ink  and  should  be  interleaved  with  the  drawings. 
Each  page  of  drawings  should  have  an  appropriate  heading. 
Do  not  crowd  your  drawings;  avoid  especially  the  promiscuous 
mixing  of  unrelated  notes  on  the  same  page.  Excellent 
directions  for  laboratory  drawing  will  be  found  in  the  first 
thirty  pages  of  Hardesty's  Laboratory  Guide  for  Histology 
('08)' and  in  Guyer's  Animal  Micrology  ('17),  pp.  159-172. 

34.  Terminology. — The  confusion  in  the  use  of  terms  has 
been  more  serious  in  neurology  than  in  most  other  departments 
of  anatomy.     The  only  widely  used  standard  is  the  official  list 
of  the  German  Anatomical  Society,  commonly  referred  to  as 
the  B  N  A  (see  Barker's  Anatomical  Terminology  and  Eycles- 
hymer's  Anatomical  Names),  and  it  is  necessary  to  be  familiar 
with  these  terms;  they  should  be  used  in  your  laboratory  notes. 
Some  of  our  anatomists,  however,  do  not  use  these  terms  con- 


THE    MAMMALIAN    NERVOUS    SYSTEM  43 

sistently.  Accordingly,  the  student  must  be  familiar  with  some 
other  of  the  more  commonly  used  names  also.  The  SNA 
terms  or  their  English  equivalents  are  used  in  this  Outline,  save 
that  dorsal  and  ventral  are  substituted  for  posterior  and 
anterior  and  that  some  fiber  tracts  (notably  in  the  spinal  cord) 
are  given  names  of  clearer  physiological  significance.  A  list  of 
synonyms  of  anatomical  terms  is  appended  to  W.  Krause's 
Handbuch  der  Anatomic,  Leipzig,  1905,  and  a  more  complete 
list  in  Eycleshymer's  work  ('17)  already  cited. 

35.  Suggestions  regarding  dissection  methods. — The  study  of 
the  internal  structure  of  the  brain  may  be  made  either  by  tear- 
ing or  teasing  with  blunt  instruments,  or  by  making  series  of 
gross  and  microscopic  sections  through  the  brain  in  various 
planes.     A  surprisingly  large  amount  of  detail  can  be  seen  in 
well-prepared  gross  sections  (cf.  Barker  and  Kyes,  '00),  but  the 
interpretation  of  this  detail  is  very  difficult  unless  the  complex 
form  relations  of  the  parts  have  been  previously  determined  by 
other  methods  of  dissection.     The  gross  and  microscopic  struc- 
ture of  the  brain  should  be  correlated  so  far  as  possible  from 
the  start,  and  an  effort  should  be  made  to  form  some  idea,  even 
though  imperfect,  of  the  functional  significance  of  every  part 
as  soon  as  it  is  observed. 

Great  care  must  be  used  in  brain  dissection.  Do  not  begin  the 
dissection  until,  by  the  study  of  the  surface  anatomy  and  of 
figures  in  text-books  and  atlases,  as  well  as  by  reading,  you 
have  a  clear  idea  of  the  relative  positions  and  connections  of  the 
deep  structures  to  be  dissected.  Sharp  instruments,  such  as 
scalpels  and  scissors,  should  be  used  only  when  indicated  in  the 
directions.  Avoid  as  far  as  possible  the  contact  of  metal  with 
the  brain  tissue.  For  teasing,  use  a  sharpened  orange-wood  or 
bone  manicure  stick.  Tracts  should  be  dissected  out  in  the 
direction  in  which  the  fibers  run,  since  teasing  at  right  angles 
breaks  the  fibers,  thus  making  it  impossible  to  confirm  their 
course,  and  finally  produces  an  untidy  dissection. 

36.  Parallel  with  the  examination  of  the  gross  anatomy  of 
each  part  of  the  brain,  microscopic  sections  should  be  studied 
illustrating  its  histological  structure.     These  sections  should 
include  transverse  sections  through  the  spinal  cord  at  four 
levels   (cervical,   thoracic,   lumbar,    and  sacral)  and  a  series 


44  LABORATORY   OUTLINE    OF  NEUROLOGY 

through  the  medulla  oblongata  and  pons.  At  least  six  levels 
of  the  medulla  oblongata  should  be  studied,  and  more  if 
possible.  Similar  sections  through  the  midbrain  and  thalamus 
are  also  very  desirable,  though  somewhat  more  difficult  to 
prepare  (cf.  Sheldon,  '14).  The  student  should  also  study  as 
many  microscopic  preparations  as  possible  of  special  regions  of 
the  brain  and  sense  organs,  particularly  of  the  spinal  cord  and 
the  cerebral  and  cerebellar  cortex,  illustrating  the  appearances 
of  particular  structures  when  prepared  by  the  methods  of 
Weigert,  Nissl,  Golgi,  Cajal,  Marchi,  etc. 

37.  If  microscopic  preparations  are  not  available,  it  will  be 
found  practicable  to  select  from  the  following  paragraphs 
those  which  apply  to  the  gross  material  only  (see  Courses 
I,  III,  IV,  and  V,  pp.  11,  12).  Gross  transverse  sections 
through  the  human  brain  at  the  levels  indicated  in  Section  62 
will  show  many  details  of  internal  structure,  including  the 
location  of  the  principal  gray  masses  and  fiber  tracts.  In  mak- 
ing the  gross  sections  the  incisions  should  be  made  parallel  to 
each  other  and  at  right  angles  to  the  long  axis  of  the  medulla 
oblongata  as  far  forward  as  the  midbrain  (levels  1  to  9,  Section 
62) .  In  front  of  this  region  the  cuts  should  no  longer  be  made 
parallel,  but  so  inclined  toward  each  other  ventrally  as  to  make 
each  slice  somewhat  wedge-shaped  with  the  large  end  of  the 
wedge  dorsal.  In  this  way  allowance  is  made  for  the  flexure  of 
the  cerebral  hemispheres  upon  the  midbrain  and  the  plane  of 
section  is  kept  approximately  transverse  to  the  curved  long  axis 
of  the  brain. 

Even  if  microscopic  sections  through  all  or  a  part  of  the  brain 
stem  are  available,  a  brain  should  be  prepared  for  demonstra- 
tion purposes  by  gross  section  as  described  above  to  facilitate 
the  localization  of  the  microscopic  sections  and  their  interpre- 
tation in  terms  of  the  external  form  of  the  intact  brain. 

If  the  laboratory  work  is  limited  to  the  study  of  gross  mate- 
rial alone,  it  is  recommended  that  the  student  read  also  those 
sections  of  the  Outline  which  give  directions  for  the  study  of 
microscopic  sections,  and  with  the  aid  of  the  references  given  at 
the  close  of  each  section  consult  in  text-books  and  atlases 
figures  of  corresponding  sections. 

The  primary  purpose  of  this  study  is  to  gain  an  understand- 


THE   MAMMALIAN   NERVOUS   SYSTEM  45 

ing  of  the  functional  connections  of  the  various  parts  of  the 
nervous  system,  and  this  end  should  be  constantly  kept  in 
mind.  Daily  consultation  of  reference  books  in  connection 
with  each  structure  studied  in  the  laboratory  is  indispensable. 
The  fiber  tracts  should  be  related  to  each  other  in  functional 
systems  of  reflex  arcs  as  rapidly  as  possible.  Compare  the 
lists  given  in  the  sections  devoted  to  the  recapitulation  of 
conduction  paths  (Sections  101  and  153). 

38.  Subdivisions  of  the  brain. — For  convenience  of  study  the 
central  nervous  system  has  been  separated  somewhat  arbi- 
trarily into  subdivisions  which  are  more  clearly  defined  in  the 
embryonic  brain.     These  subdivisions  should  be  identified  on  a 
series  of  wax  models  of  developmental  stages  of  the  human 
brain,  such  as  the  His  models  manufactured  by  Ziegler,  and 
also  on  the  adult  brains  of  man  and  other  mammals. 

The  following  references  include  accounts  of  the  develop- 
ment of  the  brain  and  the  principles  of  its  subdivision,  together 
with  illustrations  of  the  His  models:  Bailey  and  Miller  ('16), 
pp.  532-557;  Gray  ('18),  pp.  733-749;  Herrick  ('18),  Chap. 
VII;  His  ('04);  Keibel  and  Mall  ('10),  Vol.  II,  pp.  29-106; 
Piersol  ('16),  pp.  1059-1063.  Almost  every  text-book  of 
human  anatomy  and  embryology  includes  some  account  of 
these  questions  and  "pictures  of  the  models.  The  official  list 
of  B  N  A  terms  is  reprinted  in  Eycleshymer's  Anatomical 
Names  ('17)  and  also  a  translation  of  the  annotations  by  Pro- 
fessor His  on  the  neurological  terms  (pp.  153-174). 

39.  Brain  of  fetal  pig. — Take  two  pig  embryos,  about  3  cm. 
and  about  5  cm.  in  length  respectively,  which  have  been  pre- 
served in  10  per  cent,  formalin.     Dissect  out  the  brains  from 
the  side,  or  else  cut  the  embryos  in  the  median  sagittal  plane. 
The  larger  embryo  can  be  more  conveniently  dissected  and  the 
smaller  one  sectioned.     They  may  be  stained  for  five  minutes 
in  a  dilute  solution  of  methylene-blue  (about  1  part  in  10,000 
parts  water)  if  desired.     Determine  the  five  brain  vesicles  with 
the  aid  of  a  dissecting  microscope  or  a  hand  lens,  draw  them, 
and  compare  them  with  the  His  models  and  the  adult  brain. 
This  is  the  procedure  followed  in  the  Anatomical  Laboratory  of 
Johns   Hopkins    University,   for   which  we  are  indebted  to 
Dr.  E.  V.  Cowdry. 


46  LABORATORY    OUTLINE    OF   NEUROLOGY 

40.  Here  review  the  dissection  of  the  fish  brain  and  deter- 
mine the  precise  limits  of  its  chief  subdivisions  in  comparison 
with  those  of  the  embryonic  human  brain.     Note  particularly 
the  relative  size  of  the  cerebral  hemispheres  in  the  brains  of 
various  animals  and  that  certain  other  parts  of  the  brain  tend 
to  vary  with  the  size  of  the  cerebral  cortex  (thalamus,  pons, 
cerebellar   hemispheres,    etc.).     These   parts   are   known    as 
cortical  dependencies.     It  should  be  borne  in  mind  that  these 
gross  subdivisions  are  not  functionally  independent,  but  are 
connected  by  long  tracts  of  fibers. 

2.  External  Anatomy 

41.  Spinal  nerves  of  fetal  pig. — In  a  fetal  pig  of  8  or  10  cm. 
dissect  the  spinal  cord  and  nerves.     First  eviscerate  the  fetus 
through  a  median  ventral  incision.     In  the  dorsal  wall  of  the 
abdomen  note  the  spinal  nerves  segmentally  arranged  and  pass- 
ing out  from  the  midline  of  the  body.     Find  the  sympathetic 
trunk  and  its  ganglia  extending  along  either  side  of  the  ver- 
tebral  column.     Trace   the   communicating  branches    (rami 
communicantes)  by  slight  dissection  from  the  sympathetic  gan- 
glia into  the  body  wall  to  their  connections  with  the  spinal 
nerves.     Note  nerves  radiating  from  the  sympathetic  ganglia, 
many  of  which  go  to  form  the  aortic  plexus;  others  cross  the 
vertebral  column  and  connect  with  ganglia  of  the  opposite  side, 
while  still  others  pass  to  more  distal  sympathetic  ganglia  (cf. 
Section  69). 

Draw  the  dissection  at  this  stage,  showing  two  or  three  spinal 
nerves  in  position  and  their  connections  with  the  sympathetic 
ganglia  and  with  the  related  peripheral  nerves. 

42.  Spinal  cord  of  fetal  pig.— Now  place  the  fetus  on  the 
abdomen  with  the  limbs  extended.     Make  an  incision  in  the 
dorsal  midline  along  the  entire  length  of  the  body  and  remove 
the  muscles  and  other  soft  parts  adjacent  to  the  vertebral 
column,  working  laterally  from  the  midline.     Then  with  bone 
forceps  or  strong  scissors  expose  the  spinal  cord  by  clipping  the 
neural  arches  of  the  vertebrae  as  close  to  the  intervertebral  for- 
amina as  possible.     Take  care  to  avoid  crushing  or  otherwise 
injuring  the  structures  lying  in  the  vertebral  canal.     Examine 
the  meninges  of  the  spinal  cord;  then  expose  the  cord  and  dis- 


THE    MAMMALIAN   NERVOUS   SYSTEM  47 

sect  several  spinal  nerves  of  one  side  sufficiently  to  show  the 
spinal  ganglia  and  the  adjoining  portions  of  the  spinal  nerve 
trunks. 

43.  Make  a  transverse  section  through  the  fetus  in  the  tho- 
racic region  and  construct  a  diagram  magnified  two  or  four 
diameters  to  illustrate  the  relations  of  the  spinal  cord,  spinal 
nerves,    spinal   ganglia,  and  sympathetic  ganglia,  with  their 
peripheral  connections,  to  the  body  wall  as  seen  in  the  trans- 
verse section. 

44.  Spinal  cord,  gross  structure. — Note  in  the  intact  human 
spinal  cord  (medulla  spinalis)  the  following  external  features: 
the  size,  shape,  length,  segmentation,  the  cervical  and  lumbar 
enlargements  (intumescentise),  ventral  and  dorsal  nerve  roots, 
ganglia,   membranes   (meninges),   ligamentum  denticulatum. 
Determine  the  location  of  the  four  transverse  sections  of  the 
human  cord  which  have  been  distributed.     Review  from  the 
text-books  the  anatomical  formation  of  the  spinal  column, 
the  relations  of  the  cord  segments  to  their  respective  vertebrae 
(Reid's  chart),  the  blood-supply  of  the  spinal  cord,  its  method 
of  suspension  in  the  vertebral  canal,  and,  as  far  as  possible, 
the   relations   of  the   spinal  nerve  roots  to  their  peripheral 
distributions. 

Cunningham  ('15),  Figs.  459^65,  pp.  517-522,  and  pp.  685- 
753;  Morris  ('14),  pp.  752,  756,  771-775,  914,  919-921,  964- 
974;  Quain  ('09),  Vol.  Ill,  Part  1,  pp.  58-68;  Vol.  Ill,  Part  2, 
pp.  52-148;  Piersol  ('13),  pp.  1021-1028,  1054,  1278,  and  the 
following  pages;  Reference  Handbook  of  the  Medical  Sciences, 
3d  ed.,  Vol.  7,  article  Spinal  Cord;  Sobotta  ('11),  pp.  114-124; 
Spalteholz  ('09),  Vol.  Ill,  pp.  617-623;  Toldt  (r04),  pp.  752- 
759  and  810,  ff. 

45.  Brain  membranes. — Each  student  should  be  supplied  if 
possible  with  a  sheep's  brain  and  one  lateral  half  of  a  human 
brain.     The  intact  human  brain  will  first  be  examined  by  two 
students  at  adjacent  desks  before  being  cut  into  halves. 

Study  the  brain  membranes  (meninges)  and  blood  supply  of 
the  sheep's  brain,  especially  the  circle  of  Willis  (cf.  Burkholder, 
('12),  Plate  IV)  and  the  other  vessels  of  the  ventral  surface, 
and  compare  with  the  human.  Review  from  the  reference 
books  the  form  of  the  human  skull  and  its  foramina  with  their 


48  LABORATORY    OUTLINE    OF   NEUROLOGY 

contained  nerves  and  blood-vessels;  also  the  arterial  and  venous 
blood  supply  and  the  lymph  spaces  of  the  brain  and  meninges. 
See  Cunningham  ('15),  pp.  667-677  (meninges),  pp.  900-908, 
also  pp.  969-976  (blood  supply);  Gray  ('18),  pp.  872-880 
(Meninges);  Morris  ('14),  pp.  903-924;  Piersol  ('16),  pp.  730- 
753  (blood  supply),  pp.  1197-1209  (meninges);  Quain  ('09), 
Vol.  Ill,  Part  1,  pp.  320-339;  Sobotta  ('11),  pp.  188-192. 
On  the  cerebro-spinal  fluid,  see  Halliburton  ('16);  Weed  ('14, 
'17). 


vernrus 


^pons 
^trap. 

FIG.  7. — The  brain  of  the  sheep  seen  from  the  right  side.  Natural  size. 
b.ol.,  olfactory  bulb;  f.lat.,  fissura  lateralis  (Sylvii);  floe.,  flocculus;  f.rh., 
fissura  rhinalis;  g.f.i.,  gyrus  frontalis  inferior;  g.orb.,  gyrus  orbitalis;  //  to 
XII,  cranial  nerves;  lob.pir.,  lobus  piriformis  (gyrus  hippocampi);  n.ol.L, 
nucleus  olfactorius  lateralis;  pfl.,  paraflocculus;  trap.,  corpus  trapezoideum. 

46.  Surface  anatomy  of  the  brain. — With  the  intact  human 
brain  and  the  sheep's  brain  before  you,  examine  and  compare 
their  external  forms.  Now  compare  both  of  these  brains  with 
that  of  the  dogfish.  Identify  in  each  brain  the  chief  subdivi- 
sions referred  to  in  Section  38,  so  far  as  these  are  visible  from 
the  surface.  After  the  brain  has  been  cut  in  two,  as  directed 
in  Section  58,  some  of  these  subdivisions  will  be  more  clearly 
seen.  In  what  parts  of  the  brain  do  you  find  the  greatest  re- 
semblances in  the  three  species;  where  the  greatest  differences? 

Learn  the  names  of  the  larger  structures  visible  upon  the 
surface  of  the  brain,  omitting  the  minor  subdivisions  of  the 


THE    MAMMALIAN    NERVOUS    SYSTEM  49 

cerebellum  and  (for  the  present)  the  sulci  and  gyri  of  the  cere- 
bral cortex,  for  the  study  of  which  see  Sections  114  and  115. 

On  the  brain  of  the  sheep  see  Figs.  7  to  12,  and  for  additional 
illustrations  consult  Burkholder  ('12)  and  Fiske  (r!3);  for  the 
human  brain  consult  any  standard  text-books. 

47.  The  cranial  nerves. — (a)  Locate  on  both  the  sheep  and 
the  human  brains  the  roots  of  the  twelve  pairs  of  cranial  nerves. 

(b)  The  composition  of  the  cranial  nerves  of  the  dogfish  has 
been  considered  in  Sections  15  to  19,  and  this  should  here  be 
reviewed.     Even  if  the  laboratory  course  has  not  included  the 
dissection  of  the  dogfish,  these  sections  of  the  Outline  should  be 
read  at  this  time.     Chapter  IX  of  Herrick's  Introduction  ('18) 
should  also  be  carefully  read  and  the  general  principles  of  the 
analysis  of  the  cranial  nerves  into  functional  components  mas- 
tered: cf.  also  Herrick  ('18),  Chapter  V.     The  components 
of  the  cranial  nerves  of  a  number  of  vertebrates  have  been 
analyzed  microscopically.     For  an  excellent   summary   and 
discussion  of  these  studies,  which  are  of  fundamental  impor- 
tance for  the  proper  interpretation  of  the  human  nervous  sys- 
tem, see  Johnston  ('06)  and  ('09). 

(c)  Review  from  the  text-books  of  human  anatomy  the 
peripheral  distribution  of  the  cranial  nerves,  giving  especial 
attention  to  the  classification  of  the  various  roots  of  these  nerves 
into  functionally  similar  groups  or  systems  and  the  peripheral 
distribution  and  mode  of  termination  characteristic  of  each 
system.     In  addition  to  the  references  cited  in  the  preceding 
paragraph  the  following  may  be  consulted:  Bailey  ('16),  pp. 
551,  552;  Morris  ('14),  pp.  927,  ff.;  Reference  Handbook  of 
the  Medical  Sciences,  3d  ed.,  article  Cranial  Nerves. 

(d)  The  nervus  terminalis. — This  is  a  slender  nerve  associ- 
ated with  the  olfactory  nerve  which  is  not  described  in  most 
text-books  of  anatomy,  for  its  presence  in  the  human  body  has 
very  recently  been  demonstrated.     It  has  long  been  known  in 
fishes  and  can  readily  be  seen  in  a  dissection  of  the  dogfish  (cf . 
Section  17, 1) .     Peripherally  this  nerve  is  distributed  under  the 
olfactory  mucous  membrane,  but  the  exact  mode  of  ending  has 
not  been  determined.     Its  fibers  accompany  those  of  the  fila 
olfactoria,  but  do  not  enter  the  olfactory  bulb.     In  the  adult 
man  they  pass  beyond  the  olfactory  bulb  and  extend  farther 


50 


LABORATORY   OUTLINE    OP   NEUROLOGY 


backward,  usually  in  several  very  slender  strands  embedded  in 
the  pia  mater  over  the  gyms  rectus,  to  enter  the  brain  sub- 
stance at  or  near  the  anterior  border  of  the  medial  olfactory 
stria.  Ganglion  cells  are  scattered  along  their  peripheral 
course.  The  intracranial  course  of  the  nervus  terminalis  can 


nuc.  olf.  lat. 

fissura  rhinalis. 
tuberc.  olf. 


— ~"     — ~~    Bulbus  olfactorius 


tr.  olf.  med. 

tr.  olf.  intermed. 

tr.  olf.  lat. 
chiasma  opticum 
infundibulum 

tuber  cinereum 
c.  mam. 


pyramis 


n.  XII 


FIG.  8. — The  brain  of  the  sheep  seen  from  the  ventral  side.  Slightly 
reduced,  c.mam.,  corpus  mamillare;  c.trap.,  corpus  trapezoideum;  d.b.B., 
diagonal  band  of  Broca;  lob.pir.,  lobus  piriformis;  n.III  to  n.XII,  cranial 
nerves;  nuc.olf.lat.,  nucleus  olfactorius  lateralis;  ped.cer.,  pedunculus  cer- 
ebri;  tr. olf. intermed.,  tractus  olfactorius  intermedius;  tr.olf.lat.,  tractus  olfac- 
torius lateralis;  tr. olf. med.,  tractus  olfactorius  medialis;  tr.ped.tr.,  tractus 
peduncularis  transversus;  tuberc.  olf.,  tuberculum  olfactorium  (intermediate 
olfactory  nucleus,  part  of  the  anterior  perforated  space). 

usually  be  seen  in  a  formalinized  brain  with  the  aid  of  a  strong 
magnifying  glass. 

For  recent  descriptions  of  the  mammalian  nervus  terminalis 
see:  Brookover  ('14)  and  ('17);  Huber  and  Guild  ('13);  Johns- 
ton ('13)  and  ('14);  Larsell  ('18);  McCotter  ('13).  On  the 


THE    MAMMALIAN   NERVOUS   SYSTEM  51 

relation  of  a  special  part  of  the  olfactory  nerve  to  the  vomero- 
nasal  organ  (Jacobson's  organ)  see  McCotter  ('12)  and  ('17). 

48.  Brain  stem  and  cortex. — Observe  the  relations  of  the 
cerebral  cortex  (which  makes  up  the  greater  part  of  the  cere- 
bral hemispheres)  and  the  cerebellum.     With  a  scalpel  cut  off  a 
slice  about  1  cm.  thick  from  the  posterior  pole  of  the  left  cere- 
bral hemisphere  and  a  similar  slice  from  the  left  lateral  border 
of  the  cerebellum.     Compare  the  cut  surfaces  and  observe  in 
each  the  relations  of  the  superficial  gray  matter  (cortex)  to 
the  underlying  white  matter.     The  cerebral  cortex  and  cere- 
bellum make  up  the  suprasegmental  apparatus,   as  distin- 
guished from  the  spinal  cord  and  brain  stem,  or  segmental 
apparatus;  see  Herrick  ('18),  Chap.  VII,  and  A.  Meyer  ('98), 
pp.  136-147. 

The  isthmus  is  a  constriction  of  the  brain  in  front  of  the 
medulla  oblongata  and  cerebellum.  It  divides  the  brain  into 
rhombencephalon  and  cerebrum.  The  rhombencephalon  wil  be 
examined  before  the  cerebrum.  Each  of  these  subdivisions 
consists  of  a  basal  or  segmental  part  and  a  suprasegmental  part 
(cerebellum  and  cerebral  cortex  respectively).  The  supraseg- 
mental apparatus  overlaps  the  brain  base,  or  brain  stem,  whose 
functions  it  correlates. 

49.  The   rhombencephalon. — In    both  the  human  and  the 
sheep's  brains  observe  the  mode  of  attachment  of  the  cere- 
bellum to  the  medulla  oblongata,  or  bulb.     With  a  scalpel  cut 
these  attachments  (cerebellar  peduncles)  on  each  side,  remove 
the  cerebellum,  and  lay  it  aside  for  future  study,  performing 
this  operation  first  on  the  sheep's  brain,. then  on  the  human. 
These  peduncles  should  be  severed  as  high  up  as  possible, 
cutting  into  the  substance  of  the  cerebellum  somewhat  rather 
than  into  the  substance  of  the  medulla  oblongata.     In  making 
this  dissection  be  careful  not  to  injure  the  delicate  membranes 
lying  below  the  cerebellum  and  forming  the  roof  of  the  fourth 
ventricle.     This  can  readily  be  accomplished  in  the  sheep's 
brain.     Unless  the  human  brain  is  well  preserved,  these  mem- 
branes may  be  destroyed  in  this  case. 

50.  The  cavity  of  the  rhombencephalon  is  the  fourth  ven- 
tricle   (ventriculus  quartus   or  fossa  rhomboidea).     The  cere- 
bellum  itself  forms   the   roof   of   this   ventricle   for  a  short 


52 


LABORATORY   OUTLINE    OF   NEUROLOGY 


distance  between  the  cerebellar  peduncles.  In  front  of  this 
level  in  the  isthmus  region  the  roof  is  formed  by  a  thin  sheet  of 
nervous  tissue,  the  anterior  medullary  velum  (velum  medullare 
anterius).  Behind  this  level  the  roof  of  the  fourth  ventricle 
(legmen  fossce  rhomboidece)  is  a  thin  non-nervous  membrane,  a 
part  of  which  is  highly  vascular  and  much  folded;  this  is  the 


Face  and  tongue 

Head  and  eyes 

Fore  limb 

Hind  limb 

Gyrus  sylviacus 
(arcuatus) 

Gyrus  lateralis 
Gyri  mediates 


Gyrus  internus  — 


Vermis  cerebelli -vA— 


Hemisphserium 
cerebelli 


Medulla  spinalis  _ 


Gyrus  frontalis 

medialis 
Gyrus  frontalis 

superior 
Sulcus  coronalis 
]• -Sulcus  splenialis 

Fissura  ansata 
(cruciata) 

Fissura  lateralis 
(Sylvii) 

Fissura  suprasylvia 

Fissura 

longitudinalis 
Sulcus  lateralis 

Sulcus  intermedius 
Sulcus  medialis 


— '  ~  Flocculus 


—  Nervus  accessorius 

Nervus  spinalis  I 


FIG.  9. — The  brain  of  the  sheep  seen  from  the  dorsal  side.  Slightly 
reduced.  On  the  left  side  the  areas  of  electrically  excitable  motor  cortex 
are  shown  after  the  researches  of  Simpson  and  King  (1911). 


choroid  plexus  of  the  fourth  ventricle.  If  this  membrane  is 
intact,  carefully  pick  it  up  with  forceps  or  float  it  out  under 
water  and  determine  the  line  of  its  attachment  to  the  massive 
wall  of  the  medulla  oblongata  on  each  side.  This  line  of 
attachment  is  the  tcenia  of  the  fourth  ventricle  (see  Fig.  11; 
Morris  ('14),  5th  ed.,  Fig.  639;  Sobotta  ('11),  Figs.  650,  660; 
Spalteholz  ('09),  Figs.  695,  703). 


THE  MAMMALIAN  NERVOUS  SYSTEM  53 

Note  that  immediately  behind  the  cochlear  nucleus  the 
tsenia  turns  abruptly  to  the  lateral  margin  of  the  medulla  ob- 
longata,  thus  forming  the  lower  boundary  of  a  wide  expansion 
of  the  fourth  ventricle,  the  lateral  recess,  which  extends  dorsally 
over  the  cochlear  nucleus. 

51.  The  fossa  rhomboidea. — Next  remove  the  membranous 
roof  of  the  fourth  ventricle  of  the  sheep  and  examine  carefully 
the  dorsal,  lateral,  and  ventral  surfaces  of  the  medulla  ob- 
longata.     Identify  all  the  parts  named  on  Figs.  11  and  12. 

In  the  human  brain  also  remove  the  membranous  roof  of  the 
fourth  ventricle  and  compare  its  external  form  and  the  sculp- 
turing in  the  floor  of  the  fourth  ventricle  with  that  of  the 
sheep  and  of  the  dogfish  (Section  23).  The  following  refer- 
ences will  aid  in  the  interpretation  of  the  floor  of  the  fourth 
ventricle:  Cunningham  ('15),  Figs.  477,  479,  482,  pp.  542,  544, 
550  respectively;  Morris  ('14),  Figs.  631,  640,  647,  pp.  802,  814, 
821  respectively;  Piersol  ('16),  Figs.  918,  948,  949,  pp.  1067, 
1097,  1098  respectively;  Quain  ('09),  Fig.  150,  p.  136;  Rauber- 
Kopsch  ('12),  Figs.  113,  114,  pp.  99,  100;  Reference  Handbook 
of  the  Medical  Sciences,  article  Brain  Anatomy,  Vol.  II,  pp. 
283-285;  Sobotta  ('11),  Figs.  659-661;  Spalteholz  ('09),  Fig. 
698,  p.  630;  Toldt  ('04),  Figs.  1178-1181,  pp.  768,  769;  Weed 
C14a). 

52.  In  all  of  these  cases  (dogfish,  sheep,   embryonic   and 
adult  human)  there  is  a  deep  median  sulcus  in  the  floor  of  the 
fourth  ventricle.     Laterally  of  this  is  a  slender  somatic  motor 
column,  seen  as  a  continuous  ventricular  ridge  in  the  dogfish, 
but  interrupted  in  places  in  man  and  the  sheep.     In  the  latter 
cases  this  column  (the  eminentia  medialis,  B  N  A)  includes  the 
trigonum  hypoglossi,  the  funiculus  teres  (see  Fig.  11)  and  the  col- 
liculus  facialis  which  is  sometimes  called  the  eminentia  abdu- 
centis  and  below  which  are  the  VI  nucleus  and  root-fibers  of  the 
VII  nerve.     In  the  midbrain  the  III  and  IV  nuclei  also  belong 
in  this  column,   and  throughout  its  length  the  longitudinal 
medial  fasciculus  runs  immediately  below  the  ventricular  floor 
(see  Section  92). 

53.  Visceral   motor   column. — In    the    dogfish  the  visceral 
motor  nuclei  of  the  cranial  nerves  form  a  longitudinal  column 
lying  laterally  of  the  somatic  motor  column  and  somewhat 


54  LABORATOEY    OUTLINE    OF  NEUROLOGY 

deeper.  In  mammals  some  of  these  nuclei  appear  on  the 
ventricular  floor,  but  most  of  them  lie  too  deep  to  be  located 
by  surface  study.  The  ala  cinerea  (or  trigonum  vagi)  is  an 
eminence  which  marks  the  position  of  the  dorsal  motor  nucleus 
of  the  vagus  (general  visceral  efferent)  The  special  visceral 
nucleus  of  the  IX  and  X  nerves  (nucleus  ambiguus)  is  not 
visible  from  the  surface.  Similarly  the  visceral  motor  nuclei 
of  the  VII  and  V  nerves  lie  too  deep  to  be  marked  on  the  floor 
of  the  ventricle,  though  root-fibers  from  the  motor  VII  nucleus 
form  a  curious  knee-shaped  bend  (the  genu)  which  forms  a 
part  of  the  colliculus  facialis. 

54.  Sulcus  limitans. — In  embryonic  brains  there  is  a  longi- 
tudinal limiting   sulcus  which   separates  the  ventro-medial 
motor  columns  from  the  dorso-lateral  sensory  columns.     In 
the  brain  of  the  adult  sheep  this  sulcus  is  preserved  for  the 
entire  length  of  the  fossa  rhomboidea.     It  is  much  deeper  in 
two  places  than  elsewhere,  thus  forming  the  fovea  superior  and 
fovea  inferior  (Fig.  11).     The  same  relations  are  sometimes 
found  in  the  adult  human  brains,  though  here  the  middle  part 
of  the  sulcus  limitans  is  often  obliterated  by  the  vestibular 
nucleus  and  striae  medullares  acustici. 

55.  Visceral  sensory  column. — In  the  dogfish  (Section  23) 
the  visceral  sensory  nuclei  of  the  cranial  nerves  form  a  longi- 
tudinal ridge  in  the  lateral  wall  of  the  fourth  ventricle.     In 
mammals   these    nuclei   lie  deeper  in  the  substance  of  the 
medulla  and  form  the  nucleus  of  the  fasciculus  solitarius 
(Sections  84  and  110).     In  one  place  only  this  nucleus  in  man 
reaches  the  ventricular  surface,  viz.,  in  the  fovea  inferior  and 
the  lateral  border  of  the  ala  cinerea,  which,  accordingly,  con- 
tains both  visceral  motor  and  visceral  sensory  centers.     This 
implies  that  the  fovea  inferior  does  not  mark  the  exact  site 
of  the  embryonic  sulcus  limitans,  but  lies  somewhat  laterally 
of  it. 

56.  Somatic  sensory  column. — In  mammals,  as  in  the  dog- 
fish, this  column  of  the  medulla  oblongata  contains  two  clearly 
separate  regions,  (1)  the  general  somatic  sensory  centers  and 
(2)  the  area  acustica  (see  Section  57).     Only  the  first  of  these 
will  be  considered  in  this  section. 

In  either  the  sheep  or  the  human  brain  an  examination  of  the 


THE    MAMMALIAN    NERVOUS    SYSTEM  55 

spinal  cord  where  it  joins  the  medulla  oblongata  will  reveal  on 
the  dorsal  surface  the  fasciculus  gracilis  and  the  fasciculus 
cuneatus.  These  are  composed  chiefly  of  fiber  tracts  of  the 
spinal  proprioceptive  system  and  they  enter  enlargements  lying 
laterally  of  the  lower  end  of  the  fourth  ventricle  (calamus 
scriptorius),  known  respectively  as  the  clava,  or  nucleus  of  the 
fasciculus  gracilis,  and  the  tuberculum  cuneatum,  or  nucleus  of 
the  fasciculus  cuneatus.  Laterally  of  the  tuberculum  cunea- 
tum is  the  tuberculum  cinereum,  a  longitudinal  ridge  formed  by 
the  spinal  V  tract  and  its  nucleus.  These  three  eminences 
contain  centers  of  general  cutaneous  and  deep  sensibility  for 
the  trunk,  limbs,  and  head;  that  is,  in  the  aggregate  they  form 
the  general  somatic  sensory  column. 

57.  The  area  acustica. — This  is  the  special  somatic  sensory 
column.     It  comprises  the  vestibular  nucleus  in  the  floor  of 
the  fourth  ventricle  and  the   cochlear  nucleus,   a  compact 
crescent-shaped  mass  of  gray  matter  which  encircles  the  resti- 
form  body  at  the  point  where  the  latter  turns  dorsalward  to 
enter   the   cerebellum    (Fig.    11).     The   dorsal   part   of   the 
cochlear  nucleus  is  termed  tuberculum  acusticum. 

58.  Now  get  from  the  instructor  a  long,  thin  brain  knife. 
Special  knives  for  this  purpose  are  sold  by  the  manufacturers 
of  surgical  instruments,  but  a  butcher's  ham-slicer,  to  be  pur- 
chased in  the  hardware  trade,  makes  a  very  satisfactory  substi- 
tute.    This  is  a  large  butcher  knife  with  a  long  and  very  thin, 
wide  blade.     Better  still  is  a  large  steel  spatula,  or  "  pill  knife," 
such  as  druggists  use,  with  both  edges  ground  sharp.     With 
this  knife  cut  the  entire  brain  of  the  sheep  into  right  and  left 
halves.     The  incision  should  pass  through  the  longitudinal 
fissure   between   the    cerebral   hemispheres   and   should    cut 
through  the  corpus  callosum  in  the  floor  of  this  fissure,  and  then 
downward  through  the  entire  brain  stem.     Great  care  should 
be  taken  to  make  this  cut  smooth  and  exactly  in  the  median 
plane.     It  should  be  made  with  a  single  long  sweep  of  the  knife. 

Up  to  this  point  two  students  have  examined  one  human 
brain.  Now  repeat  on  the  human  brain  the  division  into  right 
and  left  halves  in  the  same  way  as  in  the  case  of  the  sheep. 
Divide  also  the  cerebellum  by  a  median  incision.  Each 
student  takes  one-half  of  the  divided  human  brain. 


56 


LABORATORY    OUTLINE    OF   NEUROLOGY 


59.  Examine  carefully  the  cut  surfaces  of  both  the  human 
and  the  sheep's  brains,  identifying  all  median  structures  thus 
brought  into  view.  Note  again  the  arrangements  of  the  chief 
subdivisions  of  the  brain  referred  to  in  Section  38.  For  the 
sheep's  brain,  see  Fig.  10.  Similar  views  of  the  human  brain 


corpus  pineale 
commissura  posterior 
collicylus  superior 


/  habenula 

com.  hah,  /  plexus  dim 
///  ^ 

/  //  /fissura  ansata 
'     '         (cruciata) 
t  M. 


lamina 

culmen  monticul 
sulcus  pnmariu 
declive  monticuli 

pyramis 

fissura  secu 
uvula 


re  cat 

\^  com.  ant 
\^  lamina  term, 
rec.  preop. 

FIG.  10. — Median  section  of  the  brain  of  the  sheep.  Slightly  reduced. 
The  exposed  ventricular  surfaces  are  stippled.  Aq.S.,  aqueductus  cerebri 
(Sylvii);  area  olf.med.,  area  olfactoria  medialis  or  nucleus  olfactorius 
medialis;  b.ol.,  bulbus  olfactorius;  can.cen.,  central  canal  of  spinal  cord; 
ch.,  chiasma  opticum;  c.mam.,  corpus  mamillare;  col.forn.,  columna  fornicis; 
com.ant.,  commissura  anterior;  com.hab.,  commissura  habenularurn ; 
c.trap.,  corpus  trapezoideum ;  f.M.,  foramen  interventriculare  (Monroi); 
Q.i.,  gyrus  intermedius;  g.marg.ant.,  gyrus  marginalis  anterior;  g.marg. 
post.,  gyrus  marginalis  posterior;  hyp.,  hypophysis;  inf.,  infundibulum; 
lamina  term.,  lamina  terminalis;  med.obl.,  medulla  oblongata;  m.i.,  massa 
intermedia;  ped.cer.,  pedunculus  cerebri;  plexus  ch.III,  plexus  chorioideus 
ventriculi  tertii;  plexus  ch.IV.  plexus  chorioideus  ventriculi  quarti;  r.c.cal., 
rostrum  corporis  callosi;  rec.cb.,  recessus  cerebelli;  rec.preop.,  recessus  pre- 
opticus;  s.pol.,  sulcus  parolfactorius;  stria  med.thal.,  stria  medullaris  thalami; 
t.ol.,  tuberculum  olfactorium  (intermediate  olfactory  nucleus);  vel.med.ant., 
velum  medullare  anterius;  v.III,  ventriculus  tertius. 


are  pictured  by  Cunningham  ('15),  Fig.  477,  p.  542;  Gray 
('18),  Figs.  715,  720;  Quain  ('09),  Fig.  132,  p.  Ill;  Rauber- 
Kopsch  ('12),  Fig.  95,  p.  77,  Fig.  97,  p.  81;  Sobotta  ('11), 
Fig.  648;  Spalteholz  ('09),  Figs.  694,  695,  pp.  625,  626;  Toldt 
('04),  Figs.  1193-1195,  pp.  776,  777. 


THE   MAMMALIAN   NERVOUS   SYSTEM 


57 


60.  Draw  the  median  surface  of  the  human  brain  (or  of  the 
sheep's  brain  if  the  human  specimen  is  not  well  preserved  or  not 
cut  in  the  exact  median  plane),  paying  particular  attention  to 


Thalarnus 


Fasciculus 
gracilis 

Fasciculus 
cuneatus 


Tsenia 
thalami 

Habenula 


Corpus 

pineale 
Corpus 

genicula- 

turn 

mediale 

Colliculus 
superior 


Colliculus 
inferior 


Brachium 

conjuncti- 

vum 
Brachium 

pontis 
Corpus 
restiforme 
Funiculus 

teres 

Ala  cinerea 
Trigonum 
hypoglossi 

Clava 

Tubercu- 
lum 
cuneatum 

Tractus 
spinalis 
trigemini 

Tractus 

spinocere- 

bellaris 

dorsalis 


FIG.   11.- — The  dorsal   surface   of   the  medulla  oblongata   and   midbrain  of 
the  sheep.      X  2. 

the  extent  and  boundaries  of  the  ventricles.  Trace  the  ven- 
tricular boundaries  from  the  interventricular  foramen  (of 
Monro)  back  to  the  central  canal  of  the  spinal  cord.  Note 
especially  the  thin  parts  of  the  ventricular  walls:  lamina 


58  LABORATORY    OUTLINE    OF   NEUROLOGY 

terminalis,  choroid  plexus  of  the  third  ventricle,  anterior 
medullary  velum,  and  membranous  roof  of  the  fourth  ventricle 
(tegmen  fossa3  rhomboidese),  the  last  two  forming  the  roof  of 
the  ventricle  above  and  below  the  cerebellum  respectively. 

The  tegmen  fossce  rhomboidece  includes  at  its  anterior  border  a 
thin  but  nervous  plate,  the  posterior  medullary  velum,  border- 
ing the  attachment  to  the  cerebellum,  and  further  spinalward 
the  convoluted  choroid  plexus  of  the  fourth  ventricle  (cf. 
Section  50).  Notice  that  the  fourth  ventricle  extends  a  short 
distance  dorsalward  into  the  cerebellum  (recessus  cerebelli) 


trped.tr 
c.geamed 


m 

FIG.  12. — The  lateral  surface  of  the  medulla  oblongata  and  midbrain  of 
the  sheep.  X  1%.  br.c.i.,  brachium  of  colliculus  inferior;  br.p.,  brachium 
pontis;  c.gen.med.,  corpus  geniculatum  mediale;  coch.,  nucleus  cochlearis; 
col.inf.,  colliculus  inferior;  col.sup.,  colliculus  superior;  c.r.,  corpus  resti- 
forme;  f.cun.,  fasciculus  cuneatus;  f.lat.,  fasciculus  lateralis;  ///  to  XII, 
cranial  nerves;  lem.L,  lemniscus  lateralis;  n.v.,  nucleus  vestibularis ;  ped. 
cer.,  pedunculus  cerebri;  pyr.,  pyramid;  trap.,  corpus  trapezoideum ;  ir. 
ped.tr.,  tractus  peduncularis  transversus;  tr.sp.cb.d.,  tractus  spino-cerebel- 
laris  dorsalis;  tr.sp.V.,  tractus  spinalis  trigemini;  tub.cun.,  tuberculum 
cuneatum;  V.m.,  motor  root  of  trigeminus;  V.s.,  sensory  root  of  trigeminus. 

and  that  it  is  only  in  this  region  that  the  cerebellum  forms  the 
true  roof  of  the  ventricle.  Note  that  the  roof  of  the  third  ven- 
tricle is  also  a  choroid  plexus  extending  from  the  pineal  body  to 
the  interventricular  foramen  and  that  a  deep  fissure,  which  is 
outside  the  brain,  extends  forward  from  the  region  of  the  ten- 
torium  cerebelli  between  this  plexus  and  the  overlying  body  of 
the  fornix.  In  the  sheep  the  medial  surface  of  the  hippocam- 
pus is  visible  within  this  fissure  (marked  "gyms  dentatus"  in 
Fig.  10).  Locate  the  attachment  of  the  choroid  plexus  of  the 


THE    MAMMALIAN    NERVOUS    SYSTEM  59 

third  ventricle  along  the  tcenia  ventriculi  tertii,  or  tcenia  thalami, 
and  note  also  that  the  plexus  itself  is  continued  through  the 
interventricular  foramen  into  continuity  with  the  lateral  cho- 
roid  plexus  within  the  ventricle  of  the  cerebral  hemisphere.  In 
a  specimen  from  which  the  septum  pellucidum  has  been  torn 
away  this  continuity  can  be  readily  observed ;  but  do  not  at 
this  time  attempt  further  dissection  of  the  lateral  choroid 
plexus  (see  Section  132). 

The  choroid  plexuses  of  the  third  and  fourth  ventricles  are 
commonly  referred  to,  as  in  the  preceding  paragraphs,  as  form- 
ing the  true  roof  of  the  brain  cavity  in  these  regions.  But 
according  to  the  more  precise  usage  of  the  B  N  A  each  of  these 
structures  is  really  composed  of  two  layers:  (1)  the  lamina 
epithelialis,  which  is  the  true -brain  wall  derived  from  the 
embryonic  neural  tube,  which  here  retains  its  embryonic 
character  as  a  non-nervous  epithelium;  (2)  the  pia  mater,  which 
is  here  highly  vascular  and  convoluted.  In  the  B  N  A  the 
term  plexus  chorioideus  is  applied  to  this  modified  pia  mater 
alone. 

3.  General  Directions  for  Microscopic  Material 

61.  The  further  study  of  the  spinal  cord  and  brain  stem  can 
best  be  carried  out  with  both  gross  and  microscopic  material, 
though  good  results  can  be  obtained  with  either  class  of  mate- 
rial alone.     If  microscopic  preparations  are  not  available,  it  will 
be  found  practicable  to  select  from  th?  following  paragraphs 
those  which  apply  to  gross  material  only.     Gross  sections 
through  the  human  brain  at  the  levels  indicated  below  will 
show  many  of  the  details  referred  to. 

62.  Drawings    of   cross-sections. — Make    an   outline  sketch, 
ventral  s'de  down,  of  each  of  four  microscopic  transverse  sec- 
tions ( Weigert  method  preferred)  through  the  spinal  cord  taken 
respectively  from  the  cervical,  thoracic,  lumbar,  and  sacral 
regions;  and  also  select  6  to  12  transverse  sections  from  the 
series  through  the  brain  stem  and  similarly  draw  each  of  these 
in  outline.     Make  these  outlines  as  accurately  as  possible  about 
six  times  natural  size,  or  those  from  the  spinal  cord  and  lower 
part  of  the  medulla  oblongata  may  be  magnified  8  diameters 
and  those  from  the  upper  levels  4  diameters.     The  sketches  of 


60  LABORATORY   OUTLINE    OP   NEUROLOGY 

the  sections  should  include  the  outlines  of  a  few  only  of  the 
more  important  features,  such  as  the  inferior  olives,  to  serve 
as  points  of  reference.  The  following  levels  are  recommended : 

(1)  Upper  cervical  cord.     See  Bruce  ('92),  Fig.  1,  Plate  XIII; 
Bruce  ('01),  Plates  I-VIII;  Cunningham  ('15),  Fig.  466;  Piersol 
('16),  Fig.  895,  p.  1041;  Rauber-Kopsch  ('12),  Fig.  206,  p.  197. 

(2)  Lower  part  of  decussation  of  pyramidal  tracts.     See 
Bailey  ('16),  Fig.  333,  p.  490;  Bruce  ('92),  Plate  III;  Cunning- 
ham ('15),  Fig.  490,  p.  558;  Piersol  ('16),  Figs.  920,  921,  p.  1069; 
Quain  ('09),  Fig.  140,  p.  126;  Rauber-Kopsch  ('12),  Fig.  207,  p. 
197);  Sobotta  ('11),  Figs.  663,  664,  p.  172;  Spalteholz  ('09), 
Fig.  725,  p.  656;  Toldt  ('04),  Fig.  1206,  p.  786;  Villiger  ('12) 
Fig.  213,  p.  238. 

(3)  Middle  of  nucleus  of  fasciculus  gracilis  including  the 
decussation  of  the  medial  lemniscus.     See  Bailey  ('16),  Fig.  334, 
p.  492;  Bruce  ('92),  Plate  IV;  Cunningham  ('15),  Fig.  491,  p. 
559;  Piersol  ('16),  Fig.  922,  p.  1070;  Quain  ('09),  Fig.  143, 
p.  130;  Rauber-Kopsch  ('12),  Fig.  208,  p.  198;  Sobotta  ('11), 
Fig.  664;  Spalteholz  ('09),  Fig.  726,  p.  656;  Toldt  ('04),  Fig. 
1208,  p.  786;  Villiger  ('12),  Figs.  215,  216,  pp.  242-244. 

(4)  Middle  of  inferior  olive  through  vagal  nuclei.     See  Bailey 
('16),  Fig.  335,  p.  494;  Bruce  ('92),  Plate  VII;  Cunningham 
('15),  Fig.  495,  p.  561;  Piersol  ('16),  Fig.  928,  p.  1074;  Quain 
('09),  Fig.  146,  p.  132;  Rauber-Kopsch  ('12),  Fig.  214,  p.  209; 
Sobotta  ('11),  Fig.  666;  Spalteholz  ('09),  Fig.   727,  p.  657; 
Toldt  ('04),  Fig.  1209,  p.  786;  Villiger  ('12),  Fig.  219,  p.  250. 

(5)  Roots  of  VII  and  VIII  nerves.     See  Bailey  ('16),  Fig. 
340,  p.  504;  Bruce  ('92),  Plate  IX;  Cunningham  ('15)  Fig.  498, 
p.  565;  Quain  ('09),  Fig.  163,  p.  146;  Rauber-Kopsch  ('12), 
Fig.  215,  p.  210;  Sobotta  ('11),  Fig.  667. 

(6)  Colliculus  facialis  and  nucleus  of  VI  nerve.     See  Bailey 
('16),  Fig.  342,  p.  509;  Bruce  ('92),  Plate  XI ;  Cunningham  ('15), 
Fig.  531,  p.  599;  Morris  ('14),  Fig.  652,  p.  826;  Piersol  ('16), 
Fig.   933,   p.  1078;  Rauber-Kopsch  ('12),  Fig.  217,  p.  212; 
Sobotta  ('11),  Fig.  668;  Spalteholz  ('09),  Fig.  729,  p.  658; 
Toldt  ('04),  Fig.  1211,  p.  787;  Villiger  ('12),  Fig.  225;  p.  262. 

(7)  Roots  and  nuclei  of  V  nerve.     See  Bailey  ('16),  Fig.  343, 
p.  511;  Bruce  ('92),  Plate  XII;  Cunningham  ('15),  Fig.  500,  p. 
568;  Piersol  ('16),  Fig.  935,  p.  1080;  Quain  ('09),  Fig.  164,  p. 


THE    MAMMALIAN    NERVOUS    SYSTEM  61 

148;  Rauber-Kopsch  ('12),  Fig.  220,  p.  216;  Spalteholz  ('09), 
Fig.  730,  p.  658;  Villiger  ('12),  Fig.  226,  p.  264. 

(8)  Inferior  colliculus.     See  Bruce  ('92),  Plate  XXIII;  Cun- 
ningham ('15),  Fig.  520,  p.  587;  Piersol  ('16),  Fig.  960,  p.  1109; 
Quain  ('09),  Fig.  212,  p.  204;  Rauber-Kopsch  ('12),  Figs.  224, 
225,  p.  220;  Sobotta  ('11),  Fig.  652;  Spalteholz  ('09),  Fig.  732, 
p.  659;  Toldt  ('04),  Fig.  1213,  p.  788;  Villiger  ('12),  Fig.  229, 
p.  270. 

(9)  Superior  colliculus.     See  Bailey  ('16),  Fig.  355,  p.  525; 
Bruce  ('92),  Plates  XXIV,  XXV,  XXVI;  Cunningham  ('15), 
Fig.  521,  p.  587;  Edinger  ('11),  Figs.  220,  227;  Morris  ('14), 
Fig.  662,  p.  838;  Quain  ('09),  Fig.  213,  p.  205;  Rauber-Kopsch 
('12),  Fig.  227,  p.  223;  Sobotta  ('11),  Fig.  651;  Toldt  ('04), 
Fig.  1215,  p.  789;  Villiger  ('12),  Fig.  230,  p.  272. 

(10)  Medial  geniculate  body  and  red  nucleus.     See  Luciani 
('15),Vol.  Ill,  Fig.  244,  p.  489;  Piersol  ('16),  Fig.  963,  p.  1114; 
Quain  ('09),  Fig.  213,  p.  205;  Rauber-Kopsch  ('12),  Fig.  228, 
p.  224;  Spalteholz  ('09),  Fig.  733,  p.  660;  Toldt  ('04),  Fig.  1218, 
p.  791;  Villiger  ('12),  Fig.  231,  p.  274. 

(11)  Middle  of  thalamus.     See  Bailey  ('16),  Fig.  357,  p.  533; 
Piersol  ('16),  Fig.  967,  p.  1120,  and  Fig.  974,  p.  1126;  Quain 
('09),  Fig.  261,  p.  261;  Rauber-Kopsch  ('12),  Fig.  127,  p.  Ill; 
Sobotta  ('11),  Fig.  646;  Toldt  ('04),  Fig.  1219,  p.  792. 

(12)  Upper  part  of  thalamus  behind  the  anterior  commissure. 
See  Quain  ('09),  Fig.  300,  p.  316;  Toldt  ('04),  Fig.  1220,  p.  792. 

Put  each  outline  on  a  separate  sheet  and  fill  in  additional 
details  at  a  later  time  as  directed  below.  Study  the  surface 
contour  of  each  section  drawn,  and  b#  comparison  with  the 
external  form  of  the  cord  and  brain  determine  the  approximate 
location  of  the  section.  An  intact  brain  or  medulla  oblongata 
should  be  at  hand  during  this  comparison.  In  each  outline 
identify  and  label  every  superficial  structure  which  is  visible 
in  the  gross  specimen.  The  finished  drawings  will  include  only 
selected  details  of  the  structures  visible  in  the  sections.  Do 
not  complete  the  drawing  of  each  cross-section  before  passing  on 
to  the  next;  but  study  each  fiber  tract  or  nucleus  as  a  whole, 
following  it  throughout  the  series  of  sections  and  entering  it 
upon  the  drawing  of  each  level  in  which  it  appears,  as  directed 
below,  until  all  the  tracts  to  be  studied  have  been  entered  upon 


62  LABORATORY   OUTLINE    OF   NEUROLOGY 

the  sketches.  In  these  sketches  each  tract  and  nucleus  should 
in  general  be  entered  on  one  side  only,  so  as  to  avoid  unnec- 
essary complexity  in  the  finished  drawings.  In  general  the 
ascending  tracts  should  be  entered  on  the  right  side  and  the 
descending  tracts  on  the  left  side.  Of  course,  tracts  which 
decussate  will  appear  on  one  side  in  part  of  the  levels  and  on  the 
other  side  in  other  levels. 

The  separate  tracts  and  centers  may  well  be  drawn  in  differ- 
ent colors  of  wax  crayons.  In  the  illustrations  of  the  func- 
tional analysis  of  the  peripheral  nerves  in  the  literature  certain 
systems  'of  nerve  components  are  generally  conventionally 
colored,  and  on  the  basis  of  that  usage  the  following  color 
scheme  is  suggested.  For  the  basis  of  the  classification  em- 
ployed, see  Sections  15  to  19,  47,  52  to  57,  67,  and  Herrick  ('18), 
Chapters  V  and  IX. 

General  somatic  afferent: 

Exteroceptiye  (general  cutaneous) yellow 

Proprioceptive  (muscle  sense,  etc.)  and  all  afferent 

cerebellar  connections orange 

Special  somatic  afferent: 

Vestibular  (special  proprioceptive) brown 

Auditory  (cochlear)  and  optic green 

General  and  special  visceral  afferent  (afferent  sympa- 
thetic connections,  gustatory  and  olfactory) red 

General  visceral  efferent   (pre-  and  post-ganglionic 

sympathetic  fibers) purple 

Special  visceral  efferent.  v light  blue 

Somatic   efferent,   including   all  efferent   cerebellar 

tracts dark  blue 

Correlation  tracts black 

Do  not  ink  the  drawings  at  first,  but  indicate  the  outlines  of 
tracts,  etc.,  lightly  in  pencil;  then,  when  all  the  sections  have 
been  studied  as  directed  in  Sections  63  to  101,  and  the  neces- 
sary corrections  made,  review  each  section  and  enter  upon  its 
drawing  any  additional  details  desired,  such  as  the  positions 
of  gray  centers,  nerve-roots,  correlation  tracts,  etc.  See  that 
each  drawing  is  fully  labeled.  Finally,  the  drawings  may  be 
inked  in  if  desired.  (For  another  illustration  of  this  method  of 
laboratory  drawing,  see  Lineback,  1917.) 

Throughout  the  study  of  the  microscopic  cross-sections  keep 
in  mind  the  external  form  of  the  brain  in  the  region  studied  and 


THE    MAMMALIAN   NERVOUS   SYSTEM  63 

constantly  refer  to  the  intact  human  brain  for  the  relations  of 
the  nerve-roots  and  other  external  landmarks. 

(During  the  examination  of  these  sections  it  will  be  helpful 
for  the  instructor  to  demonstrate  with  the  projection  lantern  all 
of  the  sections  to  be  studied  and  point  out  some  of  the  more  im- 
portant structures.  Individual  tracts  should  be  followed 
through  the  series  of  sections,  passing  the  entire  series  in  review 
many  times  for  this  purpose.) 

4.  Internal  Structure  of  the  Spinal  Cord 

63.  General  histology  of  the  neuron. — (a)  Procure  from  the 
slaughter-house  a  portion  of  the  spinal  cord  of  a  freshly  killed 
beef  (the  cord  of  any  other  one  of  the  larger  mammals  will 
answer) .  Each  student  should  dissect  out  a  small  portion  of 
the  substance  of  the  ventral  gray  column  (ventral  horn)  and 
tease  it  out  with  needles  on  a  clean  glass  slide  until  it  is  spread 
in  a  thin  layer.  Cover  the  fresh  tissue  with  a  few  drops  of  a 
solution  of  methylene-blue  (1  part  to  10,000  parts  of  water) 
and  stain  for  fifteen  minutes.  Rinse  off  the  stain,  add  a  drop  of 
water,  and  cover  with  a  cover-slip.  Examine  with  low  and 
high  powers  of  the  microscope  and  draw  a  typical  neuron  with 
its  processes. 

(b)  Now  lay  out  all  of  the  slides  of  stained  and  permanently 
mounted  sections  of  the  spinal  cord  supplied  in  the  loan  collec- 
tion of  microscopic  material  and  examine  them  to  get  a  general 
view  of  its  internal  structure.     Compare  sections  through  the 
spinal  cord  prepared  by  different  histological  methods  (Wei- 
gert,  Nissl,  Golgi,  Cajal,  etc.)  and  note  which  histological  ele- 
ments are  best  revealed  by  each  of  the  methods  used.     Draw 
on  a  large  scale  typical  neurons  from  the  ventral  gray  column 
from  several  of  these  preparations.     Look  up  the  technic  em- 
ployed in  these  methods  and  the  purposes  for  which  each  is 
best  adapted.     On  the  study  of  pathological  degenerations  and 
the  embryological  development  of  fiber  tracts  see  Section  68 
(b)  and  (c).     A  thorough  neurological  study  of  any  part  re- 
quires the  use  of  several  histological  methods,  since  each  of 
them  is  specific  for  some  elements  only  of  the  tissue. 

(c)  Literature  on  the  neuron:  Barker  ('10),  Chapters  I  to 


G4  LABORATORY    OUTLINE    OP   NEUROLOGY 

IV;  Herrick  ('18),  Chapter  III;  Meyer  ('98);  Quain  ('09),  Vol. 
3,  Pt.  1,  pp.  21-42;  Starr,  Strong  and  Learning  ('96). 

64.  Make  a  composite  drawing  of  one-half  of  a  section  of  the 
spinal  cord  from  Weigert  and  Nissl  (or  toluidin  blue)  sections 
to  show  the  arrangement  of  both  white  matter  and  nerve-cells. 
See  Herrick  ('18),  Figs.  57,  58;  Morris  ('14),  Fig.  616,  pp.  778, 
779;  Villiger  ('12),  Fig.  94,  p.  91.  Draw  the  outline  and  the 
details  of  the  white  matter  from  a  Weigert  section  and  the 
details  of  the  gray  matter  from  a  Nissl  section.  Label  fully  all 
parts,  particularly  the  cell  clusters  (" nuclei").  Note  the  rela- 
tions of  the  non-nervous  elements  (ependyma,  blood-vessels, 
connective  tissue),  neurons,  their  cell  bodies  (perikarya)  and 
processes,  and  the  myelinated  nerve-fibers.  In  the  gray 
matter  (substantia  grisea)  identify  and  designate  the  columns : 
columna  grisea  ventralis  (ventral  horn),  columna  grisea  later- 
alis  (lateral  horn),  columna  grisea  dorsalis  (dorsal  horn),  the 
substantia  gelatinosa  of  Rolando,  the  nucleus  thoracalis  in  the 
thoracic  region  (nucleus  dorsalis  Clarkii  of  the  B  N  A,  posterior 
vesicular  column  of  Clarke,  Clarke's  column),  the  reticular 
formation  (formatio  reticularis) .  Identify  the  commissures: 
commissura  ventralis  alba;  commissura  ventralis  grisea;  com- 
missura  dorsalis. 

The  substantia  alba  (white  matter)  of  each  side  is  divided 
anatomically  by  the  emerging  nerve-roots  into  three  portions 
named  respectively  funiculus  dorsalis,  lateralis,  and  ventralis 
(Herrick  ('18),  Fig.  57).  These  funiculi  are  further  subdivided 
topographically  into  fasciculi  (fasc.  ventro-lateralis,  etc.)  which 
are  usually  made  up  of  fibers  of  diverse  sorts.  The  real  units  of 
spinal  cord  structure  are  the  tracts,  each  of  which  is  composed  of 
fibers  of  like  connections  and  functions.  (Neurologists  often 
use  the  words  funiculus,  fasciculus,  and  tract  as  synonyms, 
with  resulting  confusion.)  Your  preparations  present  no  ana- 
tomical boundaries  of  the  fasciculi  and  tracts.  They  have 
been  determined  by  physiological  experimentation  and  the 
study  of  degenerations  following  pathological  lesions. 

65.  Neurons  of  the  cord. — Lay  out  before  you  the  four  out- 
line sketches  through  the  spinal  cord  in  the  cervical,  thoracic, 
lumbar,  and  sacral  regions,  which  have  already  been  drawn. 
Now  in  the  Nissl  (or  toluidin  blue)  sections  of  the  cord  note  the 


THE   MAMMALIAN   NERVOUS   SYSTEM  65 

distribution  of  nerve-cells  in  both  the  dorsal  and  ventral  gray 
columns  at  each  of  these  levels  and  compare  in  detail  the  group- 
ing of  the  cell  bodies  in  the  ventral  columns.  Draw  these 
groups  of  cells  in  the  four  outline  sketches  of  the  spinal  cord. 
The  ventro-medial  group  of  neurones  supplies  the  muscles  of 
the  back,  the  dorso-lateral  and  ventro-lateral  groups  chiefly  the 
muscles  of  the  limbs,  and  the  intermedio-lateral  groups  the 
motor  sympathetic  fibers  (see  Barker  ('01),  pp.  883-914;  Bruce 
('01) ;  Cunningham  ('15),  Fig.  467,  p.  525;  and  Fig.  468,  p.  529, 
also  summary  on  p.  527;  Curtis  and  Helmholz  ('11);  Herrick 
('18),  Fig.  59;  Piersol  ('16),  Figs  895-901,  pp.  1041-1046; 
Quain  ('09),  Fig.  112,  p.  78;  Rauber-Kopsch  ('12),  Figs.  35- 
64,  pp.  39^42. 

On  the  neurons  of  the  dorsal  gray  columns  and  their  connec- 
tions consult  Ramon  y  Cajal  ('09),  Vol.  I,  pp.  307-340. 

66.  The   spinal   cord   performs  two   important   groups   of 
functions:  (1)  it  contains  the  central  mechanisms  of  the  intrin- 
sic   spinal    reflexes;    (2)    it  serves  as  a  path  of  conduction 
between  the  sensory  and  motor  spinal  nerves  and  the  higher 
correlation  centers  of  the  brain.     For  a  list  of  the  tracts  belong- 
ing to  the  second  group,  see  Section  101.     Here  attention 
should  be  directed  to  the  intrinsic  reflex  connections  of  the  cord. 
(On  this  subject  see  the  very  interesting  cases  reported  by 
Riddoch,  1917.)     The  cell  bodies  of  the  neurons  involved  in 
these  reflexes  lie  in  the  gray  matter,  and  their  axons  form  the 
greater  part  of  the  fasciculus  proprius,  through  which  reflex 
impulses  are  transmitted  in  both  ascending  and  descending 
directions  between  the  different  levels  of  the  cord.     With  the 
aid  of  your  reference  books  build  up  a  clear  picture  of  the  mode 
of  connection  of  these  neurons  in  typical  spinal  reflexes.     See 
Herrick  ('18),  Figs.  60,  61;  Herrick  and  Coghill  ('15);  Howell 
('18),    Chapters  VII,   VIII;  Morris  ('14),  Fig.  610,  p.  767; 
Quain  ('09),  p.  99;  Sherrington  ('06),  Chapters  I  to  IV,  espe- 
cially the  diagram  on  p.  46;  Starling  ('15),  Chap.  VII;  Starr, 
Strong,  and  Learning  ('96). 

67.  Functional  analysis  of  the  cord. — (a)  The  classification  of 
the  functional  systems  adopted  in  this  work  should  here  be  re- 
viewed (see  Sections  15  to  19,  47,  52  to  57,  and  the  references 
there  given) .     The  somatic  sensory  systems  include  the  nerves, 

5 


66  LABORATORY    OUTLINE    OF   NEUROLOGY 

centers,  and  correlation  tracts  of  general  cutaneous  and  deep 
sensibility  (in  muscles,  joints,  etc.)  and  in  the  head  the  optic, 
auditory,  and  cerebellar  systems.  These  are  all  concerned 
with  the  adjustment  of  the  body  to  its  external  environment. 
They  fall  into  two  subdivisions:  (1)  exteroceptive,  and  (2) 
proprioceptive  (see  Herrick  ('18),  Chapters  V  and  IX;  Sherring- 
ton  ('06)  Chapter  IV),  whose  conduction  pathways  and  corre- 
lation centers  are  distinct.  The  exteroceptive  systems  respond 
to  external  excitations;  the  proprioceptive  systems  to  excita- 
tions arising  within  the  body,  but  subsidiary  to  the  somatic 
motor  reacting  system.  The  optic  and  cochlear  systems  con- 
stitute highly  differentiated  or  special  members  of  the  extero- 
ceptive series,  and  the  vestibular  system  is  similarly  a  special 
proprioceptive  apparatus. 

(b)  Review  now  the  functional  composition  of  the  spinal 
nerves  (see  Herrick  ('18),  Figs.  55  and  56)  and  master  the  topo- 
graphic relations  of  the  internal  fiber  tracts  related  to  the  vari- 
ous functional  systems.  (The  central  relations  of  the  visceral 
sensory  components  of  the  spinal  nerves  are  not  accurately 
known.)  The  primary  somatic  motor  and  visceral  motor  cen- 
ters of  the  cord  are  distinct  and  are  easily  recognized  in  Nissl 
preparations.  The  somatic  motor  neurons  lie  in  the  ventral 
gray  column  and  the  visceral  motor  in  the  intermedio-lateral 
column  (see  Herrick  ('18),  Fig.  56). 

68.  (a)  Locate  with  the  aid  of  the  reference  books  the  course 
of  the  exteroceptive  spinal  lemniscus  tracts  for  touch,  tempera- 
ture, and  pain,  and  of  the  proprioceptive  systems  (dorsal  funi- 
culi  and  spino-cerebellar  tracts).  See  Herrick  ('18),  Chapter 
VIII,  and  especially  Figs.  59,  63,  and  64;  on  the  general  somatic 
systems  Chapter  XI  should  also  be  read  in  this  connection. 
Howell  ('18),  Chap.  VIII;  Starling  ('15),  Chap.  X. 

(b)  If  pathological  preparations  illustrating  degenerations  of 
spinal  cord  tracts  are  available,  these  should  be  studied  at  this 
time.     Consult  the  larger  text-books  of  neurology,  and  espe- 
cially those  of  neuropathology.     (Later  sections  relating  to 
the  tracts  of  the  brain  may  be  illustrated  in  the  same  way 
in  any  cases  where  pathological  microscopic  preparations  are 
available.) 

(c)  Valuable  information  regarding  the  courses  of  the  fiber 


THE    MAMMALIAN   NERVOUS    SYSTEM  67 

tracts  of  the  cord  and  brain  has  been  gained  by  embryological 
methods.  Some  functional  systems  of  fiber  tracts  mature 
earlier  than  others.  Fetal  spinal  cords  of  man,  pig,  or  any 
other  mammal  taken  at  successive  periods  from  the  age  when 
myelinated  fibers  first  appear  up  to  birth  and  stained  by  the 
Weigert  method  will  demonstrate  the  sequence  of  myelina- 
tion  of  the  spinal  tracts.  See  Barker  ('01),  pp.  424^437;  His 
('04). 

5.  Sympathetic  Nervous  System 

69.  At  this  time  the  student  should  consult  his  reference 
books  and  so  become  familiar  with  the  general  pattern  of  the 
sympathetic  nervous  system  and  its  relations  with  the  cerebro- 
spinal  system.     The  sympathetic  trunk  and  its  connections 
with  the  spinal  nerves  have  already  been  seen  (Section  41). 
The  following  references  are  suggested:  Barker  ('16),  Fig.  552, 
p.  269;  Cunningham  ('15),  pp.  679-682,  753-767;  Edinger  ('11), 
pp.  96-105;  Gray  ('18),  pp.  970-989;  Herrick  ('18),  Chap. 
XVI;  Howell  ('18),  Chap.  XII;  Huber  ('97);  Johnston  ('06), 
Chap.  XII;  Langley  ('00,  'OOa,  and  '03);  Luciani  ('15),  Vol. 
Ill,  Chap.  VI,  pp.  359-378;  Morris   ('14),  pp.   1026-1047; 
Piersol   ('16),  pp.   1353-1375;  Quain   ('09),  pp.   1-3,   13-20; 
Sobotta  ('11),  pp.  238-246;  Starling  ('15),  Chap.  XIX;  Stewart 
('18),  Chap.  XVII. 

6.  The  Medulla  Oblongata 

70.  The    somatic    sensory    systems.— (a)     Here   familiarize 
yourself  from  the  reference  books  with  the  somatic  sensory 
nerve-endings  in  the  skin,  subcutaneous  tissues,  muscle  spin- 
dles, tendons,  joints,  etc.     See  Herrick  ('18),  Chap.  V;  Barker 
('01))  pp.  361-421;  Cunningham  ('15),  pp.  856-866;  Piersol 
('16),  pp.  1014-1020;  Quain  ('09),  Vol.  3,  Pt.  1,  pp.  44-52; 
and  all  works  on  histology. 

(b)  Now  review  again  the  superficial  landmarks  of  the  ven- 
tricular and  lateral  surfaces  of  the  human  medulla  oblongata, 
with  special  reference  to  the  underlying  functional  columns  (see 
Sections  51  to  57).  General  somatic  sensory  fibers  for  cutane- 
ous and  deep  sensibility  of  the  head  are  found  in  the  V,  IX, 
and  X  cranial  nerves  (Herrick  ('18),  Chap.  XI),  and  the  special 


68  LABORATORY   OUTLINE    OF   NEUROLOGY 

somatic  cochlear  (Herrick  ('18),  Chap.  XIII)  and  vestibular 
(Herrick  ('18),  Chap.  XII)  are  represented  in  the  VIII  nerve* 
The  connections  of  these  systems  will  next  be  taken  up,  to- 
gether with  the  cerebral  portions  of  the  spino-cerebral  tracts 
whose  spinal  parts  have  already  been  mentioned.  The  cere- 
bellum, which  is  a  derivative  of  the  somatic  sensory  column, 
will  be  examined  later,  and  the  composition  of  its  peduncles 
summarized. 

71.  The   general  cutaneous  system. — The   cutaneous   fibers 
from  the  face  enter  the  brain  by  the  V  nerve ;  a  smaller  number 
by  the  IX  and  X  nerves.     The  cell  bodies  of  these  fibers  are 
located  respectively  in  the  semilunar  (V),  superior  (IX)  and 
jugular  (X)  ganglia.     The  fibers  of  the  sensory  V  root  in  part 
end  in  the  chief  sensory  V  nucleus  dorso-medially  of  the  super- 
ficial origin  of  the  root,  but  most  of  them  turn  abruptly  spinal- 
ward  and  thus  form  the  spinal  V  tract,  whose  fibers  form  an 
eminence  on  the  lateral  surface  of  the  oblongata — the  tuber- 
culum  cinereum  or  tubercle  of  Rolando. 

72.  Gross  preparation  of  the  spinal  V  tract. — On  the  right 
half  of  the  brain  of  the  sheep  locate  the  V,  IX,  and  X  roots 
(Figs.  7,  8,  12)  and  the  tuberculum  cinereum.     Now  with  a 
wooden  dissector  begin  at  the  lower  border  of  the  V  root  and 
carefully  scrape  away  the  transverse  fibers  of  the  pons  and  the 
trapezoid  body  until  the  longitudinal  fibers  of  the  spinal  V 
tract  lying  immediately  internal  to  them  are  exposed.     Con- 
tinue the  dissection  spinalward  by  gently  teasing  off  the  super- 
ficial external  arcuate  fibers  (see  Section  90).     Careful  scraping 
in  the  longitudinal  direction  with  an  orange-wood  stick  sharp- 
ened to  a  slightly  rounded  chisel  edge  will  readily  expose  the 
whole  length  of  the  spinal  V  tract  to  its  terminus  in  the  cer- 
vical cord.     In  its  spinal  course  its  fibers  become  superficial. 

A  similar  dissection  can  readily  be  made  on  the  human 
brain  also,  though  the  larger  size  of  the  pons  makes  it  necessary 
to  cut  through  the  large  mass  of  the  transverse  pons  fibers 
below  the  V  root  with  a  sharp  knife  in  order  to  expose  the  spinal 
V  fibers.  This  dissection,  however,  should  not  be  made  on  the 
same  specimen  which  is  to  be  used  for  the  optional  dissections 
of  the  oblongata  (Sections  102-111). 

73.  Microscopic  study  of  the  V  roots. — In  the  microscopic 


THE    MAMMALIAN   NERVOUS    SYSTEM  69 

sections  find  the  sensory  V  root  in  the  pons  region  (see  the  lefer- 
ences  in  Section  62  (7)),  and  follow  its  fibers  backward  into  the 
spinal  V  tract.  Only  a  part  of  the  sensory  V  root-fibers  enter 
this  tract.  Others  enter  the  chief  sensory  V  nucleus,  which  lies 
dorsally  of  the  spinal  V  tract  at  the  level  of  entrance  of  the  fibers 
of  the  V  nerve  and  forward  (rostrally)  of  this  level.  The  chief 
sensory  nucleus  of  the  V  nerve  and  the  spinal  V  nucleus  (sub- 
stantia  gelatinosa  of  Rolando),  which  accompanies  the  spinal 
V  tract,  are  the  terminal  nuclei  of  the  general  cutaneous  com- 
ponents of  the  cranial  nerves.  These  nuclei  and  the  spinal  V 
tract  should  be  located  and  entered  in  the  drawings  of  all  sec- 
tions in  which  they  occur. 

A  few  general  cutaneous  fibers  enter  the  spinal  V  tract  and 
its  nucleus  from  the  IX  and  X  roots  also,  but  these  are  usually 
not  evident  in  the  sections.  The  motor  nucleus  of  the  V  nerve 
will  be  seen  lying  medially  of  the  chief  sensory  V  nucleus  and  it 
may  be  drawn  in  at  this  time.  Golgi  sections  show  that  some 
peripheral  sensory  V  fibers  end  in  the  motor  V  nucleus,  thus 
providing  a  direct  reflex  connection  between  the  skin  of  the 
face  and  mouth  and  the  jaw  muscles.  Neurons  of  the  spinal  V 
nucleus  effect  the  connection  between  the  peripheral  cutaneous 
fibers  of  the  spinal  V  tract  and  the  motor  nuclei  of  the  VII,  IX, 
and  X  nerves. 

74.  Trigeminal  lemniscus. — The  ascending  secondary  fibers 
from  the  chief  sensory  V  and  spinal  V  nuclei  to  the  somesthetic 
nuclei   of   the   thalamus    (lateral   and   related   nuclei)    form 
two  tracts,  both  of  which  are  called  the  trigeminal  lemniscus. 
Their  fibers  cannot  easily  be  traced  in  either  gross  or  micro- 
scopic preparations. 

For  diagrams  showing  the  positions  of  the  V  nuclei  and  their 
connections  with  other  centers  in  the  brain,  see  Bailey  ('16), 
Fig.  344,  p.  512;  Herrick  ('18),  Figs.  64,  71,  73,  75,  77,  78,  81; 
Gray  ('18),  Figs.  696-698;  Morris  ('14),  Fig.  654,  p.  828;  Quain 
('09),  Vol.  3,  Pt.  1,  Figs.  170,  171,  172,  175,  176;  Villiger  ('12), 
Figs.  163,  164. 

75.  The  Mesencephalic  V  root. — The  fibers  of  this  root  can 
easily  be  recognized  in  the  microscopic  sections;  see  Herrick 
('18),  Fig.  75,  and  the  references  cited  in  Section  62  (8)  and  (9). 
The  root-fibers  for  the  motor  and  chief  sensory  V  nuclei  form  a 


70  LABORATORY    OUTLINE    OF   NEUROLOGY 

layer  of  white  matter  separating  these  nuclei.  From  the  dorsal 
border  of  this  layer  the  fibers  of  the  mesencephalic  root  can  be 
followed  in  the  series  of  sections  forward  and  dorsalward  to  take 
their  positions  along  the  lateral  wall  of  the  aqueduct  of  Sylvius; 
here  they  extend  through  the  entire  length  of  the  midbrain. 
These  fibers  are  the  innermost  myelinated  fibers  in  this  region 
and  they  are  of  very  large  size,  though  few  in  number.  Most 
of  them  are  descending  fibers  arising  from  the  cells  of  the 
mesencephalic  V  nucleus,  which  can  be  seen  in  favorable  prepa- 
rations as  a  row  of  large  flask-shaped  nerve-cells  accompanying 
the  tract.  Others  ascend  from  cell  bodies  lying  in  the  semi- 
lunar  ganglion.  This  root  of  the  V  nerve  has  often  been  re- 
garded as  motor  and  is  so  described  in  many  works;  but  its 
sensory  character  is  now  well  established,  though  the  functions 
of  its  ascending  and  descending  fibers  are  not  understood.  In 
the  guinea-pig  the  descending  fibers  enter  the  muscular  branches 
for  the  masseter,  pterygoid  and  temporal  muscles  (Allen) 
and  probably  serve  the  muscle  sense. 

See  Allen  ('19),  Herrick  ('18),  Chap.  IX;  Johnston  ('05); 
Morris  ('14),  Fig.  654,  p.  828;  Otto  May  and  Victor  Horsley, 
('10). 

76.  The  dorsal  funiculi  of  the  cord. — In  the  gross  specimens 
both  of  the  human  and  the  sheep's  brain  identify  the  fasciculus 
gracilis  and  the  clava,  into  which  its  fibers  run  to  end  among  the 
cells  of  the  underlying  nucleus  of  the  fasciculus  gracilis.  Iden- 
tify also  the  fasciculus  cuneatus  and  the  tuber culum  cuneatum, 
within  which  lies  the  nucleus  of  the  fasciculus  cuneatus. 

Now  examine  the  microscopic  sections  of  the  human  brain  in 
the  region  of  transition  between  spinal  cord  and  medulla  oblon- 
gata  and  locate  all  of  the  structures  mentioned  in  the  preceding 
paragraph.  See  lists  of  references  under  required  drawings, 
Section  62  (1),  (2),  and  (3).  Follow  the  fibers  of  the  fasciculus 
gracilis  and  fasciculus  cuneatus  downward  through  the  four 
levels  of  the  spinal  cord  and  enter  them  in  your  sketches  of 
these  levels.  Then,  beginning  at  the  upper  end  of  the  cord, 
follow  these  fasciculi  upward  into  their  nuclei  under  the  clava 
and  tuber  culum  cuneatum  respectively,  where  their  fibers  end. 
The  axons  arising  from  the  cells  of  these  nuclei  form  the 
medial  lemniscus  (fillet). 


THE    MAMMALIAN    NERVOUS   SYSTEM  71 

77.  The  medial  lemniscus. — These  fibers  immediately  de- 
scend from  their  nuclei  to  cross  ventrally  of  the  ventricle  to  the 
other  side  of  the  brain,  thus  forming  the  decussation  of  the  lem- 
niscus.    This   tract   after   its   decussation    can   be   followed 
through  the  series  of  sections  as  far  as  the  thalamus.     In  the 
lower  part  of  the  medulla  oblongata  these  fibers  will  be  found 
in  the  interolivary  space  near  the  median  plane   (Herrick 
CIS),  Figs.  64,  72,  73).     They  are  bounded  ventrally  by  the 
cortico-spinal  (pyramidal)  tract,  and  dorsally  by  the  tecto- 
spinal  tract.     Dorsally  of  the  latter  is  the  longitudinal  medial 
fasciculus.     At  the  level  of  the  pons  the  medial  lemniscus  be- 
gins to  turn  laterally  and  in  the  midbrain  it  lies  dorsally  of  the 
substantia  nigra  (Herrick  ('18),  Fig.  75).     In  sections  through 
the  midbrain  and  thalamus  these  fibers  can  readily  be  followed 
forward  to  their  termination  in  the  lateral  and  associated 
somesthetic  nuclei  of  the  thalamus  (Herrick  ('18),  Figs.  77,  78, 
and  79).     The  medial  lemniscus  carries  general  proprioceptive 
nervous  impulses  from  the  spinal  cord  to  the  thalamus. 

Identify  the  medial  lemniscus  in  the  sections  and  draw  it  into 
the  outlines  as  far  forward  as  the  material  provided  will  permit. 
See,  in  addition  to  the  figures  cited  in  the  previous  paragraph, 
Section  62  (1)  to  (11);  Cunningham  ('15),  Fig.  579,  p.  651; 
Morris  ('14),  Fig.  632,  p.  803;  Piersol  ('16),  Fig.  964;  Sabin 
('01),  Plates  V,  VII;  Spalteholz  ('09),  Fig.  752,  p.  675;  Villiger 
('12),  Figs.  154,  155,  pp.  167,  168.  Directions  for  the  dissec- 
tion of  the  medial  lemniscus  of  man  will  be  found  in  Section 
108. 

78.  The  spinal  lemniscus. — The  ascending  secondary  path- 
way for  exteroceptive  sensibility  (touch,  temperature,  pain) 
from  the  trunk  and  limbs  is  the  spinal  lemniscus,  or  spino- 
thalamic  tracts.     There  are  two  of  these  tracts  in  the  cord,  the 
tractus  spino-thalamicus  dorsalis  for  pain  and  temperature, 
and  the  tractus  spino-thalamicus  ventralis  for  touch  and  pres- 
sure (Herrick  ('18),  Fig.  63).     In  the  medulla  oblongata  these 
accompany  the  ventral  spino-cerebellar  tract  (Herrick  ('18), 
Fig.  73)  and  in  the  midbrain  they  join  the  lateral  lemniscus 
(Herrick  (18),  Fig.  75). 

It  is  difficult  to  demonstrate  these  tracts  in  either  gross  or 
microscopic  material.  From  your  reference  books  learn  their 


72  LABORATORY    OUTLINE    OF    NEUROLOGY 

courses  and  enter  them  in  the  outline  drawings  of  the  cross- 
sections  in  their  appropriate  places  so  far  as  these  can  be 
ascertained. 

79.  Summary  of  secondary  general  somatic  sensory  tracts. — 
The  general  somatic  sensory  centers  and  tracts  of  the  brain 
which  have  now  been  analyzed  comprise  the  spinal  V  tract  and 
its  nucleus,  the  chief  sensory  V  nucleus,  the  mesencephalic  V 
tract  and  nucleus,  the  dorsal  funiculi  and  medial  lemniscus,  and 
the  spinal  lemniscus.     The  centers  mentioned  receive  all  fibers 
of  non-visceral  cutaneous  and  deep  sensibility  from  the  head, 
trunk,  and  limbs  except  those  serving  the  muscle-sense  from  the 
extrinsic  eye-muscles.     Fibers  of  this  character  are  present  in 
the  III,    IV,   and   VI   cranial  nerves,   but  of  their  central 
connections  nothing  is  known. 

From  these  primary  sensory  centers  connections  are  made 
through  the  reticular  formation  (see  Section  89)  with  neighbor- 
ing motor  centers  for  local  reflexes.  All  ascending  tracts  of  the 
second  order  from  the  primary  sensory  centers  to  the  thalamus 
are  termed  lemnisci.  The  trigeminal  lemniscus  and  the  spinal 
lemniscus  carry  exteroceptive  nervous  impulses  (general  so- 
matic sensory  series) .  Proprioceptive  reactions  are  served  by 
(1)  the  dorsal  funiculi  of  the  cord  and  medial  lemniscus,  (2) 
vestibular  system,  and  (3)  the  cerebellar  connections.  The 
first  of  these  three  belongs  in  the  general  somatic  sensory  series, 
the  second  in  the  special  somatic  sensory  series,  while  the  cere- 
bellum is  the  general  co-ordination  center  for  both  of  these 
series. 

The  papers  of  Head  and  his  associates  (see  Head  and 
Thompson  ('06),  and  Head  and  Holmes  ('11)),  may  profitably 
be  read  at  this  time;  also  Johnston  ('06),  Chapter  VI. 

80.  Organ  of  hearing. — If  microscopic  sections  are  available, 
study  the  cochlea  and  spiral  organ  (organ  of  Corti) .     Accounts 
of  the  structure  and  functioning  of  the  internal  ear  may  be 
found  in  most  of  the  standard  text-books.     See  Bailey  ('16), 
pp.  580-590;  Cunningham  ('15),  pp.  843-854;  Herrick   ('18), 
Chap.   XIII;   Howell    ('18),   Chap.   XX;   Morris    ('14),   pp. 
1092-1096;  Starling   ('15),  pp.  505-519;  Stewart   ('18),    pp. 
1065-1075.     For  special  reference,  the  literature  cited  at  the 
end  of  Chapter  XIII  (Herrick,  '18)  is  recommended,  particu-- 


THE   MAMMALIAN   NERVOUS   SYSTEM  73 

larly  the  papers  of  Hardesty  (J08a)  and  ('15),  Prentiss  ('13), 
Shambaugh  ('07)  and  ('08),  and  Van  der  Stricht  ('18). 

81.  Gross  preparation  of  the  cochlear  nerve  and  its  connec- 
tions.— In  the  gross  specimens  locate  the  inferior  peduncle  of 
the  cerebellum  (corpm  restiforme),  which  connects  the  dorso- 
lateral  wall  of  the  medulla  oblongata  with  the  cerebellum. 
This  is  crossed  immediately  behind  the  cerebellum  by  the  dor- 
sal cochlear  root  and  nucleus  of  the  VIII  nerve  (called  the  tuber- 
culum  acusticum) .  Find  this  structure  in  both  the  human  and 
the  sheep's  brain.  Immediately  ventro-laterally  of  the  dorsal 
cochlear  nucleus  at  the  point  where  the  cochlear  root  of  the  VIII 
nerve  enters  the  brain  is  found  the  ventral  cochlear  nucleus. 

Root-fibers  of  the  cochlear  nerve  terminate  in  both  the  dorsal 
and  the  ventral  cochlear  nuclei.  Fibers  of  the  central  acoustic 
path  leave  these  nuclei  by  two  chief  tracts.  From  the  ventral 
nucleus  they  enter  the  trapezoid  body  (corpus  trapezoideum) , 
which  can  be  seen  in  the  sheep's  brain  as  a  wide  transverse  band 
on  the  ventral  surface  immediately  below  the  pons.  In  the 
human  brain  these  fibers  are  covered  by  the  fibers  of  the  pons 
and  cannot  be  seen  without  dissection  of  the  pons.  From  the 
dorsal  cochlear  nucleus  the  secondary  acoustic  path  passes 
medialward  along  the  surface  of  the  floor  of  the  fourth  ven- 
tricle, thus  forming  the  striae  medullares  acusticse,  which  are 
Very  conspicuous  in  the  human  medulla  oblongata,  but  less  so 
in  the  sheep.  The  further  course  of  the  ventral  acoustic  tract 
can  readily  be  dissected  in  the  sheep's  brain.  Having  crossed 
the  midplane  in  the  trapezoid  body,  they  enter  or  pass  close  to 
the  superior  olive  and  then  turn  forward  to  form  the  chief  com- 
ponent of  the  lateral  lemniscus  (lateral  fillet) ,  which  terminates 
in  the  inferior  colliculus  and  medial  geniculate  body. 

On  the  left  half  of  the  sheep's  brain,  which  has  been  divided 
in  the  median  plane  (see  Figs.  7,  8,  11,  12)  locate  the  root  of  the 
cochlear  nerve  and  its  nuclei.  The  connection  of  the  ventral 
cochlear  nucleus  with  the  trapezoid  body  farther  ventrally  can 
readily  be  demonstrated.  Now  observe  the  relations  of  the 
pons  and  the  brachium  pontis  and  of  the  brachium  conjunc- 
tivum  (superior  cerebellar  peduncle). 

The  fibers  of  the  latter  will  be  seen  to  be  directed  forward, 
medialward,  and  ventralward.  On  the  lateral  surface  of  the 


74  LABORATORY    OUTLINE    OF    NEUROLOGY 

brain  (see  Fig.  12,  lem.l.)  immediately  in  front  of  the  pons  and 
more  ventrally  and  superficially  than  the  fibers  of  the  brachium 
conjunct! vum  are  fibers  running  from  the  border  of  the  pons 
obliquely  forward  and  dorsalward,  thus  crossing  at  a  right  an- 
gle the  deeper  fibers  of  the  brachium  conjunctivum.  These 
superficial  fibers  compose  the  lateral  lemniscus.  They  occupy 
a  triangular  area  bounded  by  the  pons  behind,  the  basis  pedun- 
culi  (pyramidal  and  cortico-pontile  tracts)  below,  and  the 
corpora  quadrigemina  above  (Herrick  ('18),  Fig.  45). 

Beginning  at  the  cut  medial  surface,  strip  back  the  fibers  of 
the  pons  as  far  laterally  as  the  roots  of  the  V  nerve.  Immedi- 
ately ventrally  of  these  root-fibers  careful  teasing  with  a  sharp- 
ened wooden  instrument  will  show  that  some  fibers  of  the 
trapezoid  body  turn  from  the  transverse  to  the  longitudinal 
direction  and,  passing  internal  to  the  pons  fibers,  reappear  on 
the  surface  in  front  of  the  pons  as  the  lateral  lemniscus  fibers, 
to  which  reference  has  already  been  made.  At  the  point  where 
they  turn  and  are  covered  by  the  overlying  pons  fibers  a  small 
nucleus  of  gray  matter  may  be  found.  This  is  the  superior 
olive.  By  gentle  teasing  the  lateral  lemniscus  fibers  may  be 
followed  from  the  level  of  the  pons  forward  and  dorsalward. 
Some  enter  the  medial  geniculate  body  of  the  thalamus  and 
some  enter  the  inferior  colliculus.  The  latter  are  interrupted 
by  a  synapse  here  and  the  acoustic  path  is  then  continued  for- 
ward through  the  brachium  of  the  inferior  colliculus  to  enter 
the  medial  geniculate  body  in  company  with  the  component 
first  described. 

The  secondary  acoustic  path  is  thus  seen  to  ascend  from  the 
cochlear  nuclei  of  one  side  by  way  of  the  lateral  lemniscus  to  the 
medial  geniculate  body  of  the  thalamus  of  the  opposite  side. 
Some  of  these  fibers  enter  the  thalamus  directly  and  some  are 
first  interrupted  by  a  synapse  in  the  inferior  colliculus. 

For  the  dissection  of  the  lateral  lemniscus  in  the  human 
brain,  see  Section  106. 

82.  Microscopic  study  of  the  cochlear  nuclei  and  lateral  lem- 
niscus.— Now  in  the  microscopic  sections  of  the  human  brain 
stem  locate  the  structures  described  in  the  last  section  (see 
Section  62  (5)). 

Identify  the  dorsal  and  ventral  cochlear  nuclei  and  the  striae 


THE    MAMMALIAN    NERVOUS    SYSTEM  75 

medullares  acusticse.  The  fibers  of  the  trapezoid  body  may 
not  be  easily  distinguished  from  the  deepest  fibers  of  the  pons 
which  lie  ventrally  of  them.  The  superior  olive  is  a  small  gray 
nucleus  lying  deeper  than  any  of  these  fibers  and  laterally  of 
the  great  medial  lemniscus  tract  (medial  fillet).  If  the  lateral 
lemniscus  is  not  easily  identified  in  this  region,  locate  it  in  sec- 
tions at  the  level  of  the  upper  border  of  the  pons  and  trace  it 
back  to  the  superior  olive.  In  sections  through  the  midbrain 
the  lateral  lemniscus  can  readily  be  followed  to  its  termina- 
tions in  the  medial  geniculate  body  and  inferior  colliculus,  and 
the  fibers  from  the  later  to  the  medial  geniculate  body  in  the 
brachium  of  the  inferior  colliculus  are  also  easily  identified. 
Diagrams  illustrating  the  connections  of  the  cochlear  nuclei 
with  other  centers  of  the  brain  are  given  in  many  texts.  See 
Bailey  ('16),  Fig.  338,  p.  500;  Herrick  ('18),  Fig.  96;  Morris 
('14),  Fig.  650,  p.  824;  Rauber-Kopsch  ('12),  Fig.  258,  p.  269; 
Villiger  ('12);  Fig.  165,  p.  179. 

83.  Nervus  vestibularis  and  its  nuclei. — Locate  in  your  micro- 
scopic sections  and  draw  the  vestibular  root  of  the  VIII 
nerve  and  its  nuclei  (see  Section  62  (5)  and  (6)),  viz.: 

Nucleus  n.  vestibuli  superior  (of  Bechterew). 

Nucleus  n.  vestibuli  lateralis  (of  Deiters  or  nucleus  vestibu- 
laris magnocellularis) . 

Nucleus  n.  vestibuli  medialis  (of  Schwalbe,  also  called  nu- 
cleus dorsalis,  principal  nucleus,  and  nucleus  vestibularis 
triangularis) . 

Nucleus  n.  vestibuli  spinalis. 

The  fibers  of  the  vestibular  root  pass  inward  beneath  the 
inferior  cerebellar  peduncle  (restif orme  body)  and  at  right 
angles  to  its  fibers.  The  vestibular  nuclei  lie  in  the  floor  of  the 
fourth  ventricle  medially  of  the  restif orm  body  (Herrick  ('18), 
Figs.  86  and  96).  All  of  these  nuclei  (especially  the  nucleus 
medialis)  send  fibers  into  the  reticular  formation  of  the  same 
and  the  opposite  side  for  motor  reflexes  of  the  oblongata.  Find 
in  these  sections,  if  possible,  the  fibers  which  pass  from  the  ves- 
tibular root  and  nucleus  to  the  restiforme  body  and  thence  into 
the  cerebellum — the  cerebellar  root  of  the  VIII  nerve  and  the 
vestibulo-cerebellar  tract.  These  fibers  pass  directly  dorsal- 
ward  from  the  upper  end  of  the  vestibular  nuclei  (see  Herrick 


76  LABORATORY    OUTLINE    OF   NEUROLOGY 

('18),  Fig.  86)  and  join  the  restiform  body  on  its  medial  side. 
Identify  also  the  vestibule-spinal  tract,  passing  toward  the 
spinal  cord  from  the  lateral  and  spinal  vestibular  nuclei.  It 
can  be  followed  downward  through  the  series  of  sections,  ly- 
ing in  the  angle  between  the  restiform  body  and  the  dorsal 
vagal  nuclei  (see  Herrick  ('18),  Fig.  72).  Learn  its  position 
and  enter  it  in  the  sketches  of  the  medulla  oblongata  and  cord. 

The  superior  and  medial  nuclei  send  fibers  into  the  fasciculus 
longitudinalis  medialis  (posterior  longitudinal  bundle,  see  Sec- 
tion 92).  Enter  upon  your  drawings  all  of  these  vestibular 
tracts  which  have  been  observed,  including  the  fasciculus 
longitudinalis  medialis.  See  Bailey  ('16),  Fig.  339,  p.  502; 
Howell  ('18),  Chap.  XXI,  Jones  ('18);  Piersol  ('16),  Fig.  1071, 
p.  1258;  Quain  ('09),  Fig.  158,  p.  141,  and  Fig.  181,  p.  166; 
Villiger  ('12),  Fig.  168,  p.  182. 

We  have  now  completed  our  first  survey  of  the  somatic 
sensory  systems  of  the  spinal  cord  and  the  medulla  oblongata, 
except  their  connections  with  the  cerebellum.  These  will  be 
taken  up  after  the  examination  of  the  visceral  sensory  and 
the  motor  centers  of  the  medulla  oblongata. 

84.  Visceral  sensory  system. — In  the  microscopic  sections 
identify  and  draw  the  fasciculus  solitarius  and  its  nucleus. 
(See  Section  62  (4)  and  (5)) .  This  fa*sciculus  is  made  up  chiefly 
of  root-fibers  of  the  VII,  IX,  and  X  cranial  nerves  carrying  both 
general  and  special  visceral  sensory  nervous  impulses,  the 
special  fibers  being  gustatory  in  function  (Herrick  ('18),  Fig. 
114).  Root-fibers  of  some  or  all  of  these  nerves  may  be  seen  in 
the  sections  entering  the  fasciculus.  They  arise  from  the 
geniculate  (VII),  petrosal  (IX)  and  nodosal  (X)  ganglia. 
Both  the  general  and  the  special  visceral  sensory  fibers  end  in 
the  nucleus  of  the  fasciculus  solitarius,  the  gustatory  fibers 
probably  in  its  upper  end.  In  the  region  of  the  ala  cinerea 
(Herrick  ('18),  Figs.  71  to  74)  the  nucleus  is  enlarged  dorsally 
and  comes  to  the  surface  of  the  floor  of  the  fourth  ventricle  at 
the  lateral  border  of  the  ala  cinerea.  The  fasciculus  solitarius 
and  its  nucleus  correspond  with  the  visceral  sensory  column 
seen  in  the  brain  of  the  dogfish  (Section  23).  For  the  dissec- 
tion of  the  fasciculus  solitarius  in  the  human  brain  see  Section 
110, 


THE   MAMMALIAN   NERVOUS    SYSTEM  77 

In  connection  with  this  section  read  Herrick  ('18),  Chap. 
XVII,  and  Johnston  ('06),  Chap.  IX. 

85.  The  organs  of  taste. — If  microscopic  material  showing 
the  structure  of  the  taste-buds  is  available  it  should  be  exam- 
ined in  connection  with  the  study  of  the  visceral  sensory 
system  (see  Bailey  ('16),  pp.  229-232,  593;  Cunningham  ('15), 
pp.  854-856;  Piersol  ('16),  Figs.  1193-1197).     There  has  been 
much  dispute  among  neurologists  regarding  the  nerve-roots  by 
which  taste-fibers  reach  the  brain.     The  student  should  be- 
come familiar  with  the  various  theories  (see  Gushing  ('03), 
Herrick  ('18),  Fig.  115,  and  the  accompanying  discussion). 

86.  Visceral  efferent  system. — In  the  microscopic  sections 
identify  and  draw  the  dorsal  motor  X  nucleus  under  the  ala 
cinerea.     See  Section  62  (4)  and  Herrick  ('18),  Figs.  71  to  74 
and  114.     This  is  the  general  visceral  efferent  nucleus  of  the 
vagus.     The  general  visceral  efferent  nuclei  of  the  IX  and  VII 
nerves  are  respectively  the  inferior  and  superior  salivatory 
nuclei  (see  Herrick  ('18),  Figs.  71,  73,  and  114).     These  are 
not  easily  identified  in  the  sections.     Identify  also  the  nucleus 
ambiguus  (Herrick  ('18),  Figs.  71  to  74  and  114)  and  the  chief 
motor  nuclei  of  the  VII  and  V  nerves.     These  are  the  nuclei 
of  the  special  visceral  motor  components.     Look  for  fibers 
passing  out  from  them  into  the  V,  VII,  IX,  and  X  nerves. 
Extending  from  the  nucleus  ambiguus  downward  into  the 
spinal  cord  is  the  nucleus  of  the  XI  nerve.     In  the  upper  levels 
of  the  cervical  cord  these  cells  form  the  lateral  gray  column. 
Fibers  may  be  seen  passing  directly  lateralward  from  this  nu- 
cleus into  the  spinal  roots  of  the  XI  nerve. 

Sections  of  the  midbrain  through  the  nucleus  of  the  III  nerve 
will  show  a  median  group  of  cells  of  this  nucleus,  the  nucleus 
of  Edinger-Westphal  (see  Herrick  (r!8),  Fig.  71)  which  sends 
general  visceral  efferent  fibers  to  the  ciliary  ganglion. 

Visceral  reflexes  may  be  effected  by  short  and  very  simple 
connections  between  the  afferent  visceral  sensory  fibers  termin- 
ating in  the  nucleus  of  the  fasciculus  solitarius  and  the  efferent 
visceral  fibers  arising  from  the  motor  nuclei  mentioned  in  the 
preceding  paragraphs.  The  neurons  of  the  nucleus  of  the 
fasciculus  solitarius  serve  to  connect  these  primary  centers  (see 
Herrick  ('18),  Fig.  113).  On  the  visceral  efferent  system  in 
general,  see  Johnston  ('06),  Chap.  XII, 


78  LABORATORY   OUTLINE    OF   NEUROLOGY 

87.  Somatic  motor  nuclei. — This  system  is  represented  in 
the  III,  IV,  VI,  and  XII  nerves.     These  nuclei  and  the  root- 
fibers  arising  from  them  should  be  drawn  in  the  outlines  of  the 
sections  (see  references  under  required  drawings  Section  62; 
also  Bailey  ('16),  Fig.  354,  p.  524;  Gray  ('18),  Fig.  696,  p.  781; 
Herrick  ('18),  Figs.  71,  75,  and  86,  and  the  discussion  in  Chaps. 
IX  and  XI;  Johnston  ('16),  Chap.  XI;  Morris  ('14),  Fig.  647, 
p.  821,  pp.  931,  932,  Fig.  661,  p.  837,  Fig.  663,  p.  839;  Quain 
('09),  Vol. ,3,  Pt.  1,  Fig.  150,  p.  136;  Rauber-Kopsch  ('12), 
Fig.  226,  p.  281;  Villiger  ('12),  Fig.  162,  p.  175). 

88.  Correlation  fibers   of  the   medulla   oblongata. — Afferent 
nerve-fibers  enter  the  medulla  oblongata  by  the  sensory  roots  of 
the  V  to  X  cranial  nerves  and  by  certain  tracts  from  the  spinal 
cord.     Some  of  these  fibers  effect  secondary  connections  with 
the  cerebellum  as  described  below;  some  of  the  other  connec- 
tions are  as  follows: 

The  peripheral  general  cutaneous  fibers  from  the  head  are 
discharged  into  the  chief  sensory  and  spinal  V  nuclei.  The 
axons  of  the  neurons  of  these  nuclei  in  part  connect  with  the 
various  motor  nuclei  of  the  brain-stem  for  local  reflexes,  and  in 
part  ascend  to  the  thalamus  through  the  trigeminal  lemniscus, 
as  already  mentioned. 

The  central  connections  of  the  general  proprioceptive  fibers 
of  the  head  are  unknown.  Probably  the  mesencephalic  V 
nucleus  is  related  to  this  system. 

The  special  proprioceptive  fibers  from  the  labyrinth  are  re- 
ceived by  the  vestibular  nuclei,  as  already  described ;  the  axons 
of  these  cells  reach  the  various  motor  nuclei  of  the  bulb,  the 
cerebellum  (through  the  vestibulo-cerebellar .  tract)  and  the 
spinal  cord  (through  the  vestibulo-spinal  tract) .  The  fascicu- 
lus longitudinalis  medialis  is  an  important  correlation  tract 
for  this  system  (see  Section  92). 

The  chief  central  pathway  from  the  cochlear  nuclei  is  the 
lateral  lemniscus  already  studied ;  but  in  addition  to  this  there 
are  manifold  reflex  connections  between  these  nuclei,  the  nuclei 
of  the  trapezoid  body,  the  superior  olives,  the  nuclei  of  the 
lateral  lemniscus,  and  the  inferior  colliculus  on  one  hand  and 
the  motor  nuclei  of  the  bulb  and  spinal  cord  on  the  other  hand. 
The  spinal  connection  is  chiefly  through  the  tecto-spinal  tract 
of  the  cord  (Herrick  ('18),  Fig.  59). 


THE   MAMMALIAN   NERVOUS   SYSTEM  79 

Visceral  reflexes  may  be  effected  by  short  and  very  simple 
connections  between  the  nucleus  of  the  fasciculus  solitarius  and 
the  motor  nuclei  of  the  bulb.  There  is  also  a  visceral  lemniscus 
conducting  visceral  impulses  upward  to  the  diencephalon,  but 
the  course  of  these  fibers  in  the  human  brain  is  unknown. 

89.  The  reticular  formation  (see  Herrick  ('18),  Figs.  69,  73, 
81,  and  83). — In  addition  to  the  direct  and  relatively  simple 
connections  between  the  sensory  and  the  motor  nuclei  referred 
to  in  the  preceding  sections,  there  are  more  diffuse  connections 
for  more  complex  reflexes  through  the  formatio  reticularis. 
This  is  a  complex  of  gray  with  many  bundles  of  myelinated 
fibers  running  through  it  in  the  ventro-lateral  regions  of.  the 
medulla  oblongata.     Locate  it  in  the  sections  and  indicate  it  in 
the  drawings.     This  tissue  is  reached  by  fibers  from  all  sen- 
sory nuclei  of  the  medulla  oblongata  and  the  axons  of  its  neu- 
rons are  distributed  to  the  various  motor  nuclei.     It  is  the 
direct  continuation  of  the  reticular  formation  of  the  cervical 
cord  (see  Herrick  ('18),  Fig.  58,  "processus  reticularis")  and 
its  fibers  (the  formatio  reticularis  alba)  are  functionally  similar 
to  the  fasciculi  proprii  of  the  cord. 

90.  Arcuate  fibers. — The  correlation  fibers  just  described  in 
part  connect  various  nuclei  of  the  same  side  of  the  brain,  and  in 
part  they  cross  to  the  opposite  side.     The  decussating  fibers 
are   called   arcuate   fibers.     Some   of   them    cross    obliquely 
through  the  deeper  levels  of  the  oblongata  (internal  arcuate 
fibers),  while  others  form  a  thin  but  dense  layer  of  obliquely 
transverse  fibers  on  the  extreme  outer  surface  (external  arcuate 
fibers,  see  Herrick  ('18),  Fig.  72).     Both  sorts  of  arcuate  fibers 
are  evident  in  sections  at  most  levels  of  the  medulla  oblongata. 

91.  The  spino-bulbar  tracts. — Various  ascending  tracts  from 
the   spinal  cord  to  the  brain  have  already  been   mentioned 
Some  of  these  fibers  pass  through  the  medulla  oblongata  to  end 
in  the  thalamus  and  the  cerebellum.     Others,  like  the  fascicu- 
lus   gracilis   and    fasciculus    cuneatus,    end    in    the  medulla 
oblongata  and,  after  a  synpase  here,  are  continued  upward  to 
the  thalamus  under  a  different  name.     The  fibers  of  all  of 
these  tracts  may  give  off  collaterals  into  the  gray  centers  of 
the  cord  and  the  correlation  centers  of  the  brain  stem.     Similar 
fibers  reach  the  midbrain  (tractus  spino-tectalis,  see  Herrick 


80  LABORATORY   OUTLINE    OF   NEUROLOGY 

('18),  Figs.  59  and  75.)  These  connections  serve  for  reflexes  of 
more  complex  sorts  than  can  be  effected  in  the  spinal  cord  alone, 
in  contrast  with  the  lemniscus  systems  terminating  in  the 
thalamus  and  thence  connecting  with  the  cerebral  cortex,  which 
may  serve  conscious  reactions.  The  spino-bulbar  connections 
are  diffuse  and  are  not  readily  seen  in  sections,  though  physio- 
logically they  are  important. 

92.  The  longitudinal  medial  bundle. — The  fasciculus  longi- 
tudinalis   medialis    (the  posterior  longitudinal  bundle)  is  an 
important  longitudinal  motor  co-ordination  system  which  can 
easily  be  followed  in  the  microscopic  sections  through  the 
whole  length  of  the  midbrain  and  bulb  and  downward  into  the 
fasciculus  proprius  of  the  cord.     It  is  composed   of  heavily 
myelinated  fibers  lying  near  the  median  plane  immediately 
ventrally  of  the  ventricle.     It  has  already  been  noted  in  con- 
nection with  the  vestibular  apparatus  (Section  83).     If  its 
entire  course  has  not  already  been  entered  in  the  drawings, 
this  should  be  done  now.     It  arises  in  front  of  the  III  nucleus 
and  is  related  with  all  of  the  motor  nuclei  of  the  brain  and 
spinal  cord.     It  is  used  in  conjugate  movements  of  the  eyeballs, 
in  vestibule-oculomotor  equilibratory  reactions,  and  in  many 
other  reflex  movements.     See  Barker  ('01),  Fig.  406,  p.  617; 
Bruce  ('92),  Plate  XXVII,  Fig.   1;  Cunningham  ('15),  Fig. 
524,  p.  590;  Piersol  ('16),  Fig.  965,  p.  1117. 

93.  Dissection  of  the  longitudinal  medial  bundle. — On  the 
right  side  of  the  divided  sheep's  brain  this  tract  can  be  brought 
to  view  by  gentle  scraping  in  the  longitudinal  direction  on  the 
median  cut  surface  immediately  ventrally  of  the  fourth  ven- 
tricle.    In  this  way  the  fasciculus  can  be  exposed  throughout 
the  entire  length  of  the  brain  stem. 

94.  Microscopic  study  of  the  pyrami-dal  tract. — The  tractu3 
cortico-spinalis  (fasciculus  cerebro-spinalis  of  the  B  N  A),OT 
pyramidal  tract,  is  the  great  descending  voluntary  motor  path 
between  the  motor  areas  of  the  cerebral  cortex  and  the  lower 
motor  centers.     It  can  be  readily  identified  in  the  sections 
through  the  middle  region  of  the  medulla  oblongata  (see  refer- 
ences in  Section  62),  lying  ventrally  close  to  the  median  plane 
below  the  olives.     From  the  level  of  the  olives  follow  it  upward 
also.     Immediately  below  the  pons  it  forms  a  sharp  projection 


THE   MAMMALIAN   NERVOUS   SYSTEM  81 

on  the  ventral  surface,  the  pyramid,  from  which  the  tract 
receives  its  name.  Its  fibers  can  be  followed  into  the  sub- 
stance of  the  pons.  Here,  as  the  sections  are  followed  upward, 
the  fibers  of  the  cortico-pontile  tracts  are  added  to  them,  so 
when  they  emerge  upon  the  ventral  surface  of  the  cerebral 
peduncle  above  the  pons,  the  pyramidal  fibers  form  only  the 
middle  part  of  the  basis  pedunculi,  with  cortico-pontile  fibers 
on  each  side  of  them. 

Enter  the  pyramidal  tract  in  the  sketches,  consulting  Herrick 
(J18),  Fig.  75,  for  its  position  in  the  cerebral  peduncle.  The 
following  references  are  also  suggested:  Bailey  ('16),  Fig.  331, 
p.  486;  Cunningham  ('15),  Fig.  480,  p.  545;  King  ('11);  Morris 
('14),  Fig.  664,  p.  841,  and  Fig.  706,  p.  897;  Piersol  ('16),  Fig. 
1026,  p.  1187;  Rauber-Kopsch  ('12),  Figs.  263,  264,  pp.  276, 
277;  Toldt  ('09),  Fig.  1216,  p.  790;  Fig.  1229,  p.  800;  Villiger 
('12),  Figs.  176,  179,  181,  182. 

95.  Dissection  of  the  pyramidal  tract. — The  pyramidal  tract 
can  readily  be  dissected  in  the  brains  of  the  sheep  and  of  man. 
If  only  one  human  brain  is  to  be  dissected  and  it  is  desired  to 
make  the  optional  dissections,  this  tract  should  not  be  exposed 
in  this  specimen  at  this  time  (see  Section  138). 

On  the  right  half  of  the  brain  of  the  sheep  (see  Fig.  8)  locate 
the  pyramid  on  the  ventral  surface  below  the  pons.  Strip  the 
pons  fibers  back  from  the  cut  median  surface  for  a  short  dis- 
tance so  as  to  expose  the  longitudinal  pyramidal  fibers  dorsally 
of  them.  In  the  sheep  the  pyramidal  fibers  will  be  found  to 
interdigitate  with  those  of  the  trapezoid  body  and  one  or  the 
other  of  these  systems  will  have  to  be  partially  destroyed  to 
expose  the  other.  In  following  the  pyramidal  tract  spinal- 
ward,  careful  teasing  will  separate  its  fibers  as  far  down  as 
their  decussation,  below  which  they  can  no  longer  be  dissected. 
For  their  spinal  course  see  King  ('11). 

From  the  pons  upward  the  pyramidal  tract  can  be  dissected 
through  the  cerebral  peduncle,  the  number  of  associated  cortico- 
pontile  fibers  being  much  less  than  in  man.  The  further  dis- 
section of  the  pyramidal  tract  through  the  cerebral  hemisphere 
should  be  deferred  (see  Sections  138  and  150). 

There  are  many  descending  systems  besides  the  pyramidal 
tracts;  for  an  excellent  summary  of  these  see  Rauber-Kopsch 
('12),  pp.  275-292. 


82  LABORATORY   OUTLINE   OF   NEUROLOGY 

7.  Structure  and  Connections  of  the  Cerebellum 

96.  The  cerebellar  peduncles. — There  are  three  of  these  pe- 
duncles: the  superior  (brachium  conjunctivum),  the  middle 
(brachium  pontis),  and  the  inferior  (corpus  restiforme). 

(a)  Gross  Structure. — The  cerebellar  peduncles  have  been  sev- 
ered in  both  the  human  and  the  sheep's  brain  (Section  49). 
Examine  their  cut  surfaces  on  the  dorsal  aspect  of  the  medulla 
oblongata  (for  the  sheep  see  Fig.  11).     With  the  orange- wood 
stick  separate  the  fibers  of  the  three  peduncles  from  each  other 
on  the  cut  surface  and  continue  the  separation  of  the  superior, 
and  middle  peduncles  for  ]  cm.  or  less  in  a  downward  direction. 

On  the  left  half  of  the  sheep's  brain  expose  the  inferior 
peduncle,  or  restiform  body,  by  the  removal  of  the  cochlear 
nuclei^  (cf.  Section  81)  and  tease  out  its  fibers  from  their  cut 
ends  downward  along  the  dorso-lateral  border  of  the  medulla 
oblongata.  They  cross  the  fibers  of  the  spinal  V  tract  super- 
ficially from  their  dorsal  to  their  ventral  border  and  continue 
into  the  cord  as  the  dorsal  spino-cerebellar  tract  of  Flechsig 
(see  Fig.  12). 

The  fibers  of  the  middle  peduncle,  or  brachium  pontis,  of  the 
left  side  were  partially  dissected  when  studying  the  cochlear 
nuclei  (Section  81).  Their  dissection  may  now  be  completed. 

The  superior  peduncle,  or  brachium  conjunctivum,  can  now 
be  dissected  further  to  its  decussation  in  the  cerebral  peduncle 
under  the  colliculus  superior. 

For  the  dissection  of  the  human  cerebellar  peduncles,  see 
Sections  103-105. 

(b)  Microscopic  study  of  the  cerebellar  peduncles.— In  the 
microscopic  sections  locate  the  inferior  cerebellar  peduncle 
(corpus  restiforme)   immediately  below  its  connection  with 
the  cerebellum.     Following  it  downward  it  will  be  found  to 
receive  fibers  from  the  vestibular  nucleus  (see  Section  83)  and 
the  inferior  olive  of  the  opposite  side  (olivo-cerebellar  tract; 
see  Herrick  ('18),  Figs.  72  and  87). 

Some  of  its  fibers  can  also  be  followed  downward  into  the 
spinal  cord,  where  they  are  known  as  the  dorsal  spino-cerebellar 
tract  (fasciculus  cerebello-spinalis  of  Flechsig  in  the  B  NA  list). 
For  the  courses  of  this  dorsal  spino-cerebellar  tract  (of  Flech- 
sig) and  of  the  ventral  spino-cerebellar  tract  (of  Gowers)  in 


THE    MAMMALIAN   NEKVOUS    SYSTEM  83 

the  spinal  cord  and  brain  stem,  see  Barker  ('01),  Chaps.  XL 
and  XLI;  Bailey  ('16),  Fig.  345,  following  p.  512;  Herrick  ('18), 
Figs.  59,  63,  73,  83,  87;  Morris  ('14),  Fig.  707,  p.  898;  Piersol 
('16),  Fig.  946,  p.  1905;  Quain  ('09),  Vol.  3,  Pt.  1,  Fig.  205,  p. 
198. 

In  your  sections  of  the  spinal  cord  and  brain  stem  the  fibers 
of  the  ventral  spino-cerebellar  tract  cannot  be  separately  recog- 
nized. They  ascend  in  the  lateral  funiculus  and  in  the  medulla 
oblongata  accompany  the  spinal  lemniscus  fibers  lying  super- 
ficially just  dorsally  of  the  inferior  olive.  In  transverse  sec- 
tions of  the  isthmus  region  immediately  below  the  decussation 
of  the  IV  nerves  these  fibers  can  be  recognized  for  a  short 
distance  on  the  extreme  dorso-lateral  surface  external  to  those 
of  the  brachium  conjunctivum  and  dorsally  of  those  of  the 
lateral  lemniscus.  At  this  point  they  are  turning  dorsalward 
from  the  brain  stem  to  curve  backward  into  the  substance  of 
the  cerebellum. 

The  superior  cerebellar  peduncle  (brachium  conjunctivum) 
can  be  easily  followed  in  the  sections  from  the  cerebellum  for- 
ward and  downward  into-the  midbrain  to  its  decussation  under 
the  aqueduct  of  Sylvius  and  its  termination  in  the  red  nucleus 
(nucleus  ruber)  of  the  opposite  side  (see  Morris  ('14),  Fig.  638, 
p.  811,  and  Villiger  ('12),  Figs.  178,.  179,  pp.  193,  194). 

The  brachium  pontis  is  also  easily  identified  in  the  sections. 

All  of  the  cerebellar  tracts  mentioned  in  this  section  should 
be  entered  in  your  drawings  of  the  cross-sections,  using  refer- 
ence books  to  supplement  the  incomplete  demonstrations  of  their 
courses  which  have  been  possible  in  your  microscopic  sections. 

(c)  Summary  of  the  cerebellar  peduncles. — (See  Herrick  ('18), 
Fig.  87.) 

The  inferior  peduncle  (corpus  restiforme)  is  composed  chiefly 
of  ascending  fibers  from  the  great  proprioceptive  sensory  cen- 
ters of  the  spinal  cord  (dorsal  spino-cerebellar  tract  of  Flechsig), 
from  the  inferior  olive  (olivo-cerebellar  tract),  and  from  the 
vestibular  root  and  nucleus  of  the  VIII  nerve  (vestibulo- 
cerebellar  tract). 

The  middle  cerebellar  peduncle  (brachium  pontis)  is  a  system 
of  fibers  running  from  the  nuclei  of  the  pons  to  the  opposite 
cerebellar  hemisphere.  The  nuclei  of  the  pons  receive  impor- 


84  LABORATORY    OUTLINE   OF   NEUROLOGY 

tant  descending  tracts  from  the  cerebral  cortex  (cortico-pon- 
tile  tracts).  The  fibers  of  the  brachium  pontis  arise  from 
the  nuclei  of  the  pons,  thus  transmitting  nervous  impulses  de- 
rived from  the  cerebral  cortex  to  the  cortex  of  the  opposite 
cerebellar  hemispheres. 

The  superior  peduncle  (brachium  conjunctivum)  is  the  chief 
efferent  pathway  from  the  cerebellum.  These  fibers  arise 
chiefly  from  the  dentate  nucleus  (Section  98),  enter  the  mid- 
brain,  and  cross  to  the  opposite  side  under  the  aqueduct  of 
Sylvius,  after  which  they  end  in  or  near  the  red  nucleus  (nucleus 
ruber)  under  the  superior  colliculus.  The  superior  peduncle 
also  contains  ascending  fibers  from  the  spinal  cord  (ventral 
spino-cerebellar  tract  of  Gowers). 

Between  the  superior  peduncles  is  stretched  a  thin  sheet  of 
nervous  tissue,  the  anterior  medullary  velum. 

97.  Inferior  olives,  pontile  nuclei,  arcuate  nuclei,  substantia 
nigra. — These  gray  centers  of  the  brain  stem  are  all  function- 
ally related  with  the  cerebellum.     All  of  these  nuclei  (except 
perhaps  the  arcuate)  send  fibers  to  the  cerebellar  hemisphere  of 
the  opposite  side  (see  Strong  ('15)) .     Identify  all  of  these  nuclei 
and  enter  them  in  the  sketches.     The  cerebellar  connections  of 
the  inferior  olive  (olivo-cerebellar  tract,  see  Herrick  ('18),  Figs. 
72,  83  and  87)  and  of  the  pontile  nuclei  (brachium  pontis,  see 
Herrick  ('18),  Fig.  87)  should  also  be  identified  and  indicated 
on  the  sketches.     The  inferior  olives  and  arcuate  nuclei  re- 
ceive internal  and  external  arcuate  fibers  from  the  sensory 
nuclei  of  the  oblongata.     The  inferior  olive  receives  also  a 
strong  tract  from  the  thalamus  (central  tegmental  tract)  and  a 
smaller  tract  from  the  spinal  cord  (spino-olivary  tract,  see 
Herrick  ('18),  Fig.  87).     These  cannot  be  easily  distinguished 
in  the  sections.     Its  chief  discharge  path  is  the  olivo-cerebellar 
tract  and  a  smaller  one  (the  olivo-spinal  tract)  discharges  into 
the  spinal  cord. 

98.  Cerebellar  nuclei. — In  addition  to  the  superficial  cortical 
gray  matter  of  the  cerebellum  there  are  several  deep  gray 
masses.     The  largest  of  these  is  the  dentate  nucleus  lying 
within  each  cerebellar  hemisphere,  from  whose  neurons  most 
of  the  fibers  of  the  superior  cerebellar  peduncle  arise.     Smaller 
gray  masses  are  found  under  the  vermis  near  the  roof  of  the 


THE   MAMMALIAN   NERVOUS   SYSTEM  85 

fourth  ventricle.  These  are  the  nuclei  emboliformis,  globosus, 
and  fastigii.  These  nuclei  are  not  easily  seen  in  a  dissection  of 
a  sheep's  brain,  but  may  readily  be  found  in  either  gross  or 
microscopic  sections  of  the  human  brain. 

See  Cunningham  ('15),  Figs.  511,  512,  and  535;  Morris  (14), 
Figs.  637  and  638;  Piersol  ('13),  Figs.  950  and  951;  Quain  ('09), 
Vol.  Ill,  Part  1,  Figs.  185-189;  Rauber-Kopsch  ('12),  Fig.  105; 
Sobotta  ('11),  Figs.  657  and  658;  Spalteholz  ('09),  Fig.  743; 
Toldt  ('04),  Figs.  1182-1189. 

99.  Microscopic  structure  of  the  cerebellar  cortex. — Examine 
and  draw  the  sections  of  cerebellar  cortex  provided,  and  with 
the  aid  of  your  reference  books  build  up  a  mental  picture  of  the 
connections  of  the  different  types  of  cortical  neurons.     See 
Herrick  ('18),  Fig.  89  and  the  accompanying  discussion,  and 
references  cited  at  the  end  of  Section  100. 

100.  Structure,  subdivision,  and  functions  of  the  cerebellum. 
— Compare  the  external  form  of  the  cerebellum  in  the  fish, 
sheep,  and  man,  and  note  that  variations  in  the  size  of  the  cere- 
bellar hemispheres  are   correlated  with  those  of  the  pons. 
What  are  the  fiber  connections  of  the  pons,  and  with  what  re- 
mote part  of  the  brain  is  it  in  functional  connection?     Identify 
the  vermis,   hemispheres,   and   flocculus  of  the   cerebellum. 
Arbor  vitce  is  a  name  given  to  the  appearance  of  the  cerebellar 
gray  and  white  matter  as  seen  in  median  section  of  the  vermis. 
It  is  separated  into  two  principal  subdivisions  by  the  sulcus 
primarius  (Fig.  10). 

The  cerebellum  is  a  great  proprioceptive  center  of  coordina- 
tion. We  have  already  learned  that  it  is  connected  by  afferent 
fiber  tracts  with  the  primary  basal  proprioceptive  apparatus  of 
the  spinal  cord  and  brain  stem.  And  it  is  also  intimately  re- 
lated with  the  cerebral  cortex  through  the  cortico-pontile  fiber 
tracts  (Section  96,  c).  Nervous  mechanisms  for  the  perform- 
ance of  all  simple  reflex  and  voluntary  acts  are  provided  in 
other  parts  of  the  central  nervous  system ;  but  the  participation 
of  the  cerebellum  is  necessary  for  the  performance  of  all  com- 
plex movements,  especially  for  equilibration,  motor  coordina- 
tion, and  the  maintenance  of  muscular  tone. 

The  human  cerebellum  is  subdivided  anatomically  into  a 
very  large  number  of  parts,  the  names  of  which  are  given  in  all 


86 


LABORATORY    OUTLINE    OF   NEUROLOGY 


BN  A 

Ala  lobuli  centralis 

Lobulus  centralis 

Culmen  monticuli 

Pars  anterior  lobuli 

quadrangularis 

Pars  posterior  lobuli 

quadrangularis 

Declive  monticuli 

Lobulus  semilunaris 
superior 


BOLK 
Lobus  anterior 


Sulcus  primarius 
Lobulus  simplex 
S.  pel. 
Lobulus  ansiformis 


FIG.  13. — The  human  cerebellum  from  above. 


Lobus  anterior 

Cerebellar  peduncles 
Flocculus 

Sulcus 

uvulo-nodularis 
Tonsilla 

Fissura  secunda 


Lobulus 
ansiformis 


Lobulus  centralis 

Ala  lobuli  centralis 

Brachium  pontis 

Flocculus 

Brachium 

conjunctivum 

Nodulus 

Uvula 

Tonsilla 

Lobulus  biventer 
Pyramis 

Tuber 

Lob'l.  semilun.  inf. 
Sulcus  horizontalis 
Lobulus  semilu- 
naris superior 

FIG.  14. — The  human  cerebellum  from  below. 

In  these  two  diagrams  the  principal  subdivisions  of  the  cerebellum  are 
indicated  and  the  B  N  A  names  are  designated  at  the  left.  At  the  right 
are  the  names  given  by  Bolk  to  these  structures  and  one  fissure  not  named 
by  Bolk,  the  sulcus  postclivalis  (S.pcL),  as  named  by  Symington  in  Quain's 
Anatomy.  The  sulcus  primarius  of  Bolk  and  Kuithan  is  the  same  as  the 
furcal  sulcus  of  Stroud,  the  fissura  prima  of  Elliot  Smith,  and  the  sulcus 
preclivalis  of  Symington.  The  lobulus  simplex  of  Bolk  extends  across  the 
median  plane  and  includes  the  declive  of  the  B  N  A  in  the  vermis.  The 
tonsilla  is  Elliot  Smith's  lobulus  paramedianus. 

The  functional  localization  within  the  cerebellar  cortex  as  determined 
by  Bolk,  Rynberk,  and  others  is  also  indicated  on  the  figures.  Head  move- 
ments are  controlled  in  the  lobus  anterior  of  Bolk,  i.  e.,  all  parts  in  front  of 
the  sulcus  primarius.  The  lobus  simplex  controls  neck  movements.  Arm 
and  leg  movements  are  controlled  in  the  lobus  ansiformis  and  trunk  move- 
ments in  the  inferior  vermis. 

of  the  larger  text-books  of  anatomy.  Recent  investigations  of 
the  comparative  anatomy,  comparative  embryology,  experi- 
mental physiology,  and  pathology  of  the  cerebellum  have 


THE    MAMMALIAN   NERVOUS    SYSTEM 


87 


revealed  a  rather  obscure  type  of  functional  localization  within 
the  cerebellum  which  bears  no  simple  relation  to  the  anatom- 
ical subdivisions  as  defined  in  the  B  N  A  tables. 

Broadly  speaking,  there  are  centers  within  the  cerebellar 
cortex  for  muscular  coordination  and  tonic  control  of  the  more 
cephalic  parts  of  the  body  in  the  dorsal  and  rostral  parts  of  the 
cerebellum.  Centers  for  the  similar  control  of  the  more  caudal 
muscular  complexes  extend  around  the  caudal  margin  of  the 
cerebellum  to  the  inferior  surface.  Centers  for  bilaterally 
coordinated  movements  of  paired  groups  of  muscles  are  me- 


Folium  vermis 
Declive  monticuli 


Culmen  monticuli 


Lobulus  centralis 

Velum  medullare 
anterius 

Lingula 


Tuber  vermis 


Pyramis 


^"LJLHj     Uvula 


Nodulus 

Tela  chorioidea 
ventriculi  quarti 


FIG.  15. — A  sagittal  section  through  the  vermis  of  the  human  cerebel- 
lum. The  B  N  A  names  of  the  parts  are  given  and  also  the  functional 
localization  as  determined  by  Bolk,  Rynberk,  and  others.  The  areas  of 
the  head  and  neck  extend  lateralward  as  indicated  on  Fig.  13.  The  area 
for  control  of  movements  of  the  trunk  is  limited  to  the  inferior  vermis. 
The  area  for  the  limbs  in  the  tuber  vermis  is  for  the  control  of  coordinated 
movements  of  both  members  of  a  pair,  while  the  arm  and  leg  areas  shown 
in  Figs.  13  and  14  control  the  separate  movements  of  these  limbs. 

dian  and  unpaired.  The  centers  for  the  motor  control  of  each 
limb  separately  lie  laterally  on  the  corresponding  side  of  the 
cerebellum. 

The  general  arrangement  of  these  functional  regions  is  shown 
in  Figs.  13,  14,  15  and  16,  though  many  details  are  still  ob- 
scure. In  particular,  it  has  not  been  possible  to  separate  the 
arm  areas  from  the  leg  areas  in  man;  but  experimental  studies 
on  other  mammals  suggest  that  the  leg  area  lies  inferior  to  the 
arm  area,  as  indicated  in  Fig.  14. 

The  preceding  account  of  localization  of  function  is  based 
on  the  studies  of  Bolk  and  Van  Rynberk.  More  recently 


88 


LABORATORY    OUTLINE    OF   NEUROLOGY 


Ingvar  has  restudied  the  question  and  reached  somewhat  dif- 
ferent conclusions.  The  type  of  motor  control  exercised  by 
the  cerebellum  is  evidently  very  different  from  that  of  the 
motor  centers  of  the  cerebral  cortex.  The  latter  determines 
what  movement  is  to  be  made;  the  former  appears  to  be  con- 
cerned only  with  the  synergic  control  of  the  muscles  whose 
activity  is  called  forth  by  other  centers. 


S.  preen. 

FIG.  16. — The  same  section  shown  in  Fig.  15  with  the  names  of  the 
cerebellar  fissures.  Bolk's  names  are  printed  in  full;  others  are  abbre- 
viated. Between  the  lingula  and  the  lobulus  centralis  is  the  sulcus  pre- 
centralis  (S.prcen.)  of  Symington.  Above  the  lobulus  centralis  is  the  sulcus 
postcentralis  (S.pcen.)  of  Symington,  or  fissura  preculminata  of  Elliot  Smith. 
The  sulcus  primarius  of  Bolk  is  the  fissura  prima  of  Elliot  Smith  and  the 
sulcus  preclivalis  of  Symington.  Above  the  declive  is  the  sulcus  postclivalis 
(S.pcl.)  of  Symington.  Between  the  folium  and  the  tuber  is  the  sulcus 
horizontal's  magnus  (S.h.m.)  of  Symington.  Between  the  tuber  and  the 
pyramis  is  the  sulcus  postpyramidalis  (S.ppy.)  of  Symington.  Below  the 
pyramis  is  the  fissura  secunda  of  Bolk  and  Elliot  Smith,  or  sulcus  pre- 
pyramidalis  of  Symington.  Between  the  uvula  and  the  nodulus  is  the  sulcus 
uvulo-nodularis  of  Bolk  or  sulcus  postnodularis  of  Symington.  For  a 
corresponding  section  of  the  cerebellum  of  the  sheep,  see  Fig.  10. 

The  nomenclature  of  the  cerebellum  is  in  great  confusion, 
each  investigator  having  developed  his  own  terminology. 
In  Figs.  13,  14,  15,  and  16  the  B  N  A  names  are  indicated  and 
the  names  used  by  Bolk  and  some  other  more  recent  students 
are  given  for  comparison. 

On  the  structure,  connections,  and  general  functions  of  the 
cerebellum  consult  especially  the  following  works:  Bailey 
('16),  pp.  513-520;  Cunningham  ('15),  pp.  570-581;  Herrick 
('18),  Chap.  XII;  Howell  ('18),  pp.  233-245;  Johnston  ('06), 
Chap.  XV;  Luciani  ('15);  Quain  ('09),  pp.  67-202;  Rauber- 
Kopsch  ('12),  Schaefer  ('00);  Spalteholz  ('09);  Starling  ('15), 


THE   MAMMALIAN   NERVOUS   SYSTEM  89 

Chap.  XIII;  Starr,  Strong  and  Learning  ('96);  Strong  (?15); 
Toldt  ('04). 

The  recent  investigations  bearing  on  functional  localization 
in  the  cerebellum  (Figs.  13-16)  are  numerous.  See  Andre- 
Thomas  and  Durupt  ('14);  Archambault  ('18);  Babinski  and 
Tournay  ('12);  Barany  ('12);  Black  ('16);  Bolk  ('06);  Howell 
('18),  p.  243;  Ingvar  ('18);  Jones  ('18);  Luciani  ('15);  Van 
Rynberk  ('07  and  '12) — critical  summaries  with  full  bibliogra- 
phies; Smith  ('03). 
8.  Summary  of  Spinal,  Bulbar,  and  Cerebellar  Tracts  and  Centers 

101.  Now  review  your  sketches  of  the  cross-sections  of  the 
spinal  cord  and  brain  stem,  fixing  in  mind  the  entire  course  of 
each  tract  there  represented  between  the  thalamus  and  the 
lower  end  of  the  spinal  cord.  The  individual  drawings  may 
also  be  filled  in,  if  desired,  by  the  addition  of  other  details,  and 
colored  (for  color  scheme  see  Section  62). 

In  the  accompanying  List  of  Conduction  Pathways  the  more 
important  tracts  of  the  brain  stem  are  arranged  according  to  a 
functional  classification,  and  each  neuron  of  a  conduction  path 
is  given  a  separate  entry.  The  tracts  of  the  prosencephalon 
(thalamus  and  cerebral  hemispheres)  have  not  yet  been 
studied;  but  their  names  are  entered  in  the  List,  printed  in 
black-face  type,  for  future  reference. 

Using  this  List  as  a  basis,  now  prepare  a  Table  of  Conduction 
Pathways  which  may  be  made  up  according  to  the  pattern  illus- 
trated on  page  92,  where  the  first  three  entries  of  the  List  are 
filled  into  the  Table.  The  remaining  items  of  the  List  should 
also  be  entered  in  the  Table,  giving  each  entry  of  the  List  a 
horizontal  line  in  the  Table.  In  the  first  column  of  the  Table 
in  place  of  the  name  of  the  tract  we  have  entered,  for  economy 
of  space,  simply  the  numerical  symbols  of  the  tracts  as  given  in 
the  List. 

Not  all  of  the  tracts  here  listed  can  be  demonstrated  either 
by  dissection  or  by  the  study  of  microscopic  sections  of  the  nor- 
mal nervous  system.  Their  courses  have  been  demonstrated 
by  a  combination  of  anatomical,  physiological,  and  pathol- 
ogical observations.  The  data  for  the  Table  will,  accordingly, 
be  derived  partly  from  your  laboratory  notes  and  partly  from 
the  reference  books. 


90  LABORATORY    OUTLINE    OF   NEUROLOGY 

LIST  OF  CONDUCTION  PATHWAYS 

A.    ASCENDING    (SENSORY)    SYSTEMS 

I.  General  Somatic  Sensory,  Exteroceptive 

1.  Touch  and  pressure  of  trunk  and  limbs. 

1)  Peripheral  neurons  in  spinal  nerves. 

2)  Secondary    path    in    spinal    lemniscus    (tr.    spino-thalamicus 

ventralis). 

3)  Tertiary  path  to  cortex  (projection  tract). 

2.  Pain  and  temperature  of  trunk  and  limbs. 

1)  Peripheral  neurons  in  spinal  nerves; 

2)  Secondary    path    in    spinal    lemniscus    (tr.    spino-thalamicus 

lateralis). 

3)  Tertiary  path  to  cortex  (projection  tract). 

3.  Cutaneous  sensibility  of  head. 

1)  Peripheral  neurons  in  V,  IX.  and  X  cranial  nerves. 

2)  Secondary  path  in  trigeminal  lemniscus. 

3)  Tertiary  path  to  cortex  (projection  tract). 

II.  General  Somatic  Sensory,  Proprioceptive 
1.  Muscle  sense,  etc.,  of  trunk  and  limbs. 

1)  Peripheral  neurons  in  spinal  nerves  and  dorsal  funiculi. 

2)  Thalamic  secondary  path  in  medial  lemniscus. 

3)  Tertiary  path  to  cortex  (projection  tract). 

4;   Cerebellar  secondary  path  in  dorsal  spino-cerebellar  tract. 

5)  Cerebellar  secondary  path  in  ventral  spino-cerebellar  tract. 

6)  Olivary  secondary  path  in  spino-olivary  tract  (?). 

III.  Special  Somatic  Sensory,  Proprioceptive 
1.  Vestibular  nerve. 

1)  Peripheral  neurons. 

2)  Secondary  path  to  cerebellum  by  vestibulo-cerebellar  tract. 

3)  Secondary  path  to  cord  by  vestibulo-spinal  tract. 

4)  Secondary  path  to  oculomotor  and  spinal  nuclei  by  fasciculus 

longitudinalis  medialis. 

5)  Secondary  paths  to  motor  nuclei  of  bulb  by  arcuate  fibers. 

IV.  Special  Somatic  Sensory,  Exteroceptive 

1.  Cochlear  nerve. 

1)  Peripheral  neurons. 

2)  Secondary  path  from  dorsal  nucleus,  acoustic  striae  and  lateral 

lemniscus. 

3)  Secondary  path  from  ventral  nucleus,  trapezoid  body,  and  lateral 

lemniscus. 

4)  Secondary  paths  to  motor  nuclei  of  bulb  and  midbrain. 

5)  Inferior  colliculus  to  thalamus. 

6)  Thalamus  to  cortex  (auditory  projection  tract). 

2.  Optic  system. 

1)  Receptors  (rods  and  cones). 

2)  Granule  cells  of  the  retina. 

3)  "Ganglion"  cells  of  retina. 

(a)  to  colliculus  superior. 

(b)  to  thalamus. 

4)  Reflex  path  colliculus  superior  to  cord  (tecto-spinal  tract). 

5)  Thalamus  to  cortex  (optic  projection  tract). 


THE    MAMMALIAN    NERVOUS    SYSTEM  91 

V.  General  and  Special  Visceral  Sensory 

1.  Visceral  sensory  fibers  from  sympathetic  in  spinal  nerves. 

(Secondary  connections  unknown.) 

2.  Visceral  sensory  and  gustatory  fibers  in  VII,  IX,  and  X  cranial  nerves 

and  fasciculus  solitarius. 
(Secondary  connections  unknown.) 

B.    DESCENDING    (EFFERENT)    SYSTEMS 

/.  Visceral  Efferent 

1.  General  visceral  efferent  of  spinal  cord. 

1)  Preganglionic  neurons  in  intermedio-lateral  column  of  cord. 
2)  ^  Postganglionic  neurons  in  sympathetic  ganglia. 

2.  General  visceral  efferent  of  brain. 

1)   Preganglionic  neurons  in  III  nucleus  for  ciliary  ganglion. 

2)   Postganglionic  neurons  in  ciliary  ganglion. 
3)  Preganglionic  neurons  in  superior  salivatory  nucleus  of  VII  nerve 

for  sublingual  and  submaxillary  glands. 
4)  Postganglionic  neurons  in  submaxillary  ganglion. 
5)  Preganglionic  neurons  in  inferior  salivatory  nucleus  of  IX  nerve 

for  parotid  salivary  gland. 
6)  Postganglionic  neurons  in  otic  ganglion. 

7)  Preganglionic  neurons  in  dorsal  motor  nucleus  of  vagus  and  ad- 
jacent centers  for  cardiac,  respiratory,  and  other  visceral 
reactions. 

8)  Postganglionic    neurons    in    various    sympathetic    ganglia 
associated  with  the  vagus. 

3.  Special  visceral  efferent. 

1)  Masticatory  movements  from  motor  V  nucleus. 

2)  Mimetic  movements  from  motor  VII  nucleus. 

3)  Movements  of  pharynx,  larynx,  esophagus  from  the  nucleus  am- 

biguus. 

4)  Movements  of  shoulder  from  XI  nucleus  (primitively  visceral  but 

secondarily  somatic  in  type). 

//.  Somatic  Efferent 

1.  Movements  of  eyeball  from  motor  III,  IV  and  VI  nuclei. 

2.  Movements  of  tongue  from  XII  nucleus. 

3.  Movements  of  trunk  and  limb  musculature  from  ventral  gray  column. 

4.  Reflex  motor  paths  in  cord — fasciculus  proprius. 

5.  Reflex  motor  paths  in  brain  stem. 

1)  Equilibratory  reflexes  in  tractus  vestibulo-spinalis. 

2)  Oculomotor  and  equilibratory  reflexes  in  fasciculus  longitudinalis 

medialis. 

3)  Optic  and  acoustic  reflexes  in  tractus  tecto-spinalis. 

6.  Voluntary  motor  path. 

1)  Pyramidal  tract  for  somatic  motor  centers  of  cord. 

2)  Peripheral  motor  neurons  of  spinal  nerves. 

3)  Fibers  associated  with  pyramidal  tract  for  somatic  and  special 

visceral  voluntary  motor  nuclei  of  brain  stem  (cortico-bulbar 
tracts). 

4)  Peripheral  motor  neurons  of  cranial  nerves, 

7.  Cprtico-pontile  tracts. 


92 


LABORATORY    OUTLINE    OF   NEUROLOGY 


C.    SUMMARY    OF    CEREBELLAR    CONNECTIONS 

1.  Afferent. 

1)  Tractus  spino-cerebellaris  dorsalis. 

2)  Tractus  spinp-cerebellans  ventralis. 

3)  Tractus  vestibulo-cerebellaris. 

4)  External  and  internal  arcuate  fibers. 

5)  Central  tegmental  bundle  to  inferior  olive. 

6)  Spino-olivary  tract  to  inferior  olive. 

7)  Tractus  olivo-cerebellaris. 

8)  Cortico-pontile  tracts  to  pons. 

9)  Pons  to  cerebellum  by  brachium  pontis. 

2.  Efferent. 

1)  Brachium  conjunctivum  to  nucleus  ruber. 

2)  Tractus  rubro-thalamicus  to  thalamus  and  cerebral  cortex. 

3)  Tractus  rubro-spinalis  to  cord. 

4)  Tractus  cerebello-tegmentalis  to  reticular  formation  of  brain  stem 

by  all  three  cerebellar  peduncles. 

TABLE  OF  CONDUCTION  PATHWAYS 


Name 

Cells  of 
origin 

Location 
and  course 

Decussation 

Termination 

Function 

A  I    1  1) 
A  I    1  2) 
A  I    1  3) 
A  I   2  1) 

spinal 
ganglion 

dorsal 
gray 
column 

lateral 
nucleus  of 
thalamus 

peripheral 
nerves  and 
dorsal 
roots 
ventral 
funiculus 
of  cord 

internal 
capsule 

(Table  cc 

dorsal 
gray 
column 

lateral 
nucleus  of 
thalamus 

postcentral 
gyrus 

touch  and 
pressure 

touch  and 
pressure 

touch  and 
pressure 

ventral 
commis- 
sure of 
cord 

>ntinued) 

Spaces  should  be  left  in  the  Table  for  the  prosencephalic 
tracts  printed  in  black  face  type  in  the  List,  and  these  are  to  be 
filled  in  later  in  the  course,  after  which  the  Table  will  present 
a  complete  summary  of  all  of  the  tracts  studied.  This  will  be 
of  value  for  the  final  review  and  correlation  (Section  153). 
The  relations  of  the  olfactory  tracts  are  so  complex  that  these 
may  be  omitted  from  the  Table  and  a  special  table  or  diagram 
constructed  for  them  (see  Section  130). 

This  correlation  of  the  anatomical  data  into  functional 
conduction  systems  is  the  most  important  part  of  the  course 
and  should  be  done  as  thoroughly  as  possible  and  submitted 


THE   MAMMALIAN   NEKVOUS   SYSTEM  93 

for  examination  at  the  close  of  the  course,  with  the  laboratory 
notebooks.  So  far  as  possible  indicate  the  source  of  the 
stimulus  for  each  fiber  system  (sense  organ,  motor  areas  of 
cerebral  cortex,  or  associational  nucleus,  etc.,  as  the  case  may 
be),  the  complete  course  of  the  path,  the  number  of  neurons 
involved  in  the  path  and  their  limits,  collateral  reflex  connec- 
tions, and  the  organ  at  which  the  path  terminates. 

A  useful  exercise  is  to  imagine  a  localized  injury  which  de- 
stroys a  particular  center  or  .tract  or  group  of  tracts  at  some 
point,  and  then  to  determine  what  symptoms  would  result  from 
the  injury  in  question. 

9.  Optional  Dissections  of  the  Brain  Stem 

102.  The  dissections  described  in  the  preceding  pages  can 
be  performed  upon  either  sheep  or  human  brains  ,even  though 
the  latter  be  not  very  well  preserved.     In  the  following  pages 
(Sections  103  to  111)  directions  are  given  for  a  more  complete 
dissection  of  some  of  the  structures  of  the  human  brain  stem 
than  it  is  practicable  to  carry  out  upon  the  sheep's  brain,  and 
for  these  dissections  well-preserved  human  brains  which  have 
been  hardened  in  formalin  are  necessary.     All  of  these  dis- 
sections can  be  performed  on  one  lateral  half  of  the  human 
brain,  save  that  the  connections  of  the  cerebellar  peduncles 
(Sections  103  to  105)  within  the  cerebellum  cannot  easily  be 
demonstrated  in  case  the  cerebellum  has  previously  been 
removed  as  described  in  Section  49. 

These  dissections,  being  in  some  cases  more  difficult  than 
those  previously  described,  can  best  be  done  as  a  review  exer- 
cise after  completion  of  the  preceding  exercises.  Upon  com- 
pletion of  the  dissection  of  Sections  103  to  111  preserve  the 
specimen  for  later  use  (Sections  141  to  151). 

103.  Corpus  Restiforme. — Upon  lifting  up  the  posterior  bor- 
der of  the  cerebellum  a  strong  band  of  fibers  is  seen  leaving  the 
posterior  part  of  the  cerebellar  peduncle  complex  to  turn  back- 
ward along  the  dorso-lateral  border  of  the  oblongata.     This, 
the  corpus  restiforme,  is  crossed  immediately  behind  the  cere- 
bellum by  the  dorsal  root  and  nucleus  of  the  VIII  nerve  (tuber- 
culum  acusticum).     Cut  .through  this  cochlear  VIII  root  and 
reflect  its  fibers  so  as  to  expose  the  dorsal  aspect  of  the  corpus 


94  LABORATORY    OUTLINE    OF   NEUROLOGY 

restiforme,  but  do  not  remove  the  VIII  root  and  nucleus. 
Locate  the  vestibular  (ventral)  root  of  the  VIII  nerve.  Its 
fibers  pass  under  the  corpus  restiforme  to  enter  the  vestibular 
nucleus  in  the  floor  of  the  fourth  ventricle  medially  of  the  cor- 
pus restiforme.  Vestibular  VIII  root  fibers  pass  from  the 
vestibular  root  into  the  corpus  restiforme  and  also  other  fibers 
of  the  second  order  from  the  vestibular  nucleus  to  its  medial 
border;  but  their  dissection  should  not  be  attempted  at  this 
time.  Trace  the  restiform  body  backward  and  note  that 
it  receives  external  arcuate  fibers  from  the  somatic  sensory 
region  of  the  opposite  side.  At  the  level  of  the  inferior  olive 
the  restiform  body  receives  on  its  ventral  side  a  large  tract  from 
the  olive,  but  this  cannot  be  dissected  at  this  time  without 
destroying  the  intervening  structures  ventrally  of  the  restiform 
body.  At  the  level  of  the  olive  the  restiform  body  turns 
slightly  ventralward,  crossing  superficially  the  anterior  end  of 
the  tuber culum  cinereum  (tubercle  of  Rolando  or  spinal  V 
tract),  and  then  passes  backward  ventrally  of  the  most  super- 
ficial fibers  of  the  tuberculum  cinereum.  Dissect  out  this  part 
of  the  restiform  body  and  follow  it  backward  into  the  spinal 
cord,  where  it  will  be  seen  to  form  the  dorsal  spino-cerebellar 
tract  of  Flechsig  (Section  96).  Summarizing  the  corpus  resti- 
forme, this  inferior  peduncle  of  the  cerebellum  is  composed 
chiefly  of  ascending  fibers  from  the  great  proprioceptive  sen- 
sory centers  of  the  spinal  cord,  the  inferior  olive,  and  the 
vestibular  root  and  nucleus  of  the  VIII  nerve. 

104.  Brachium  pontis. — At  the  base  of  the  cerebellum  locate 
the  fibers  of  the  brachium  pontis,  which  form  the  most  lateral 
fibers  of  the  cerebellar  peduncles.  Beginning  at  the  most 
ventral  part  of  the  pons,  gradually  tease  off  the  pons  fibers, 
stripping  them  upward  a  few  at  a  time  into  the  cortex  of  the 
cerebellar  hemisphere,  and  note  the  way  in  which  those  from 
the  anterior  (rostral)  border  of  the  pons  pass  obliquely  back- 
ward ventrally  of  those  from  the  posterior  (caudal)  border. 
Trace  these  two  layers  out  separately  and  determine  their 
distribution  in  the  cerebellar  hemisphere.  In  the  dissection  of 
the  pons  be  careful  to  preserve  the  fibers  of  the  V  nerve.  The 
brachium  pontis  fibers  as  a  whole  form  two  thick  layers,  the 
fibrae  superficiales  and  the  fibrse  profundae,  separated  by  the 


THE   MAMMALIAN    NERVOUS    SYSTEM  95 

longitudinal  fibers  of  the  pons  (pyramidal,  tract,  etc.).  The 
two  layers  of  pons  fibers  above  mentioned  belong  to  the  super- 
ficial system.  Strip  off  the  remaining  superficial  pons  fibers 
until  the  longitudinally  directed  pyramidal  tracts  are  exposed. 
The  fibers  of  the  brachium  pontis  will  be  now  seen  to  inter- 
digitate  with  the  fascicles  of  longitudinal  fibers.  These  fasci- 
culi can  be  followed  forward  into  the  midbrain  where  they  form 
the  most  ventral  fibers  of  the  pedunculus  cerebri.  Expose 
these  longitudinally  directed  fibers  for  a  short  distance  forward 
(rostrad)  and  backward  (caudad)  of  the  pons.  Do  not  com- 
pletely dissect  them,  but  leave  them  in  place  for  future  refer- 
ence. They  will  be  found  to  form  three  chief  systems.  The 
most  medial  and  the  most  lateral  bundles  of  the  fiber  complex 
which  forms  the  ventral  part  of  the  cerebral  peduncle  in  front 
of  the  pons  are  cortico-pontile  tracts  from  the  cerebral  cortex 
to  the  pontile  nuclei  (cf.  Herrick  ('18),  Figs.  75,  87),  where, 
after  a  synapse,  their  nervous  impulses  are  taken  up  by  the 
neurons  of  the  pontile  nuclei  and  carried  through  the  brachium 
pontis  to  the  cortex  of  the  opposite  cerebellar  hemisphere.  The 
middle  bundles  of  the  cerebral  peduncle  contain  the  pyramidal 
tract  (tr.  cortico-spinalis)  which  can  be  dissected  through  the 
pons  to  reappear  below  on  the  ventral  surface  of  the  oblongata 
as  the  pyramid  (pyramis) .  Its  further  course  will  be  dissected 
later.  The  chief  constituent  of  the  brachium  pontis  is  thus 
seen  to  be  a  system  of  fibers  arising  in  the  pontile  nuclei  for 
carrying  nervous  impulses  from  the  cerebral  cortex  (by  the 
cortico-pontile  tracts)  to  the  cerebellar  hemispheres  of  the 
opposite  side. 

105.  Brachium  conjunctivwn. — First  examine  the  anterior 
medullary  velum  (velum  medullare  anterius) ,  within  which  near 
the  median  plane  careful  teasing  will  reveal  a  thin  sheet  of 
fibers. 

The  brachium  conjunctivum  (superior  peduncle)  forms 
the  medial  part  of  the  cerebellar  peduncle  complex  at  the  point 
where  it  joins  the  cerebellum  (Fig.  11).  Its  fibers  are  directed 
from  the  cerebellum  forward  and  downward.  Their  further 
dissection  in  the  midbrain  (decussation  and  connection  with 
the  red  nucleus)  will  not  be  taken  up  at  this  time.  They 
should,  however,  be  dissected  up  into  the  cerebellum,  where 


96  LABORATORY  OUTLINE    OF   NEUROLOGY 

they  will  be  seen  to  connect  with  the  dentate  nucleus.  This 
tract  is  the  chief  efferent  pathway  from  the  cerebellum. 
Accompanying  the  tract  for  the  red  nucleus  are  other  descend- 
ing fibers  for  the  motor  centers  in  the  reticular  formation 
(tegmentum)  of  the  midbrain  and  oblongata  (tr.  cerebello-teg- 
mentalis)  which  cannot  easily  be  separated  from  those  for 
the  red  nucleus  (Herrick  ('18),  Fig.  87). 

There  is  another  important  component  of  the  brachium 
conjunctivum,  the  tractus  spino-cerebellaris  ventralis  of  Gow- 
ers  (see  Section  96).  At  the  lower  end  of  the  oblongata  cau- 
dad  of  the  inferior  olive  this  tract,  together  with  the  spinal 
lemniscus,  can  be  recognized,  in  the  gross  preparation,  lying 
immediately  ventrally  of  the  tr.  spino-cerebellaris  dorsalis  of 
Flechsig  and  dorsally  and  laterally  of  the  olive.  Dissect  the 
mixed  bundle  out  in  this  position  and  trace  it  forward.  It  can 
be  followed  to  a  level  near  the  pons.  Its  further  course  (which 
cannot  easily  be  dissected)  is  as  follows  (see  Section  107) :  At 
about  the  level  of  the  upper  border  of  the  pons  the  fibers  of 
the  ventral  spinocerebellar  tract  separate  from  the  lemniscus 
fibers  and  turn  abruptly  dorsal  ward,  then  backward,  to 
enter  the  brachium  conjunctivum.  Through  the  brachium 
conjunctivum  they  enter  the  vermis  of  the  cerebellum  medially 
of  the  dentate  nucleus. 

106.  The  cochlear  nuclei  and  lateral  lemniscus. — Deter- 
mine again  the  positions  of  the  cochlear  and  vestibular  roots  of 
the  VIII  nerve.  Identify  the  dorsal  and  ventral  cochlear 
nuclei.  Fibers  from  the  dorsal  nucleus  (striae  medullares 
acusticse)  can  be  followed  across  the  floor  of  the  fourth  ven- 
tricle. At  the  midline  these  fibers  decussate  and  pass  ventral- 
ward  to  the  superior  olive  of  the  opposite  side.  From  the 
ventral  cochlear  nucleus  fibers  of  the  trapezoid  body  pass 
ventralward  and  medialward,  at  first  embedded  in  the  deepest 
fibers  of  the  pons.  They  reach  the  superior  olive  of  the  same 
and  the  opposite  side.  They  can  be  dissected,  though  their 
separation  from  the  deep  fibers  of  the  pons  is  very  difficult. 
From  the  superior  olive  of  the  opposite  side  the  conduction 
path  which  continues  both  the  dorsal  and  the  ventral  cochlear 
pathways  (striae  medullares  and  trapezoid  bodies  respectively) 
is  the  lateral  lemniscus,  whose  fibers  terminate  in  the  colliculus 


THE   MAMMALIAN    NEKVOUS    SYSTEM  97 

inferior  of  the  midbrain  and  the  medial  geniculate  body  of  the 
thalamus.  This  portion  of  the  lateral  lemniscus  can  best  be 
dissected  from  above  downward  (cf.  Sections  81  and  82). 

Lift  up  the  occipital  pole  of  the  cerebral  hemisphere  and 
locate  the  superior  and  inferior  colliculi  on  the  dorsal  surface  of 
the  midbrain.  Extending  backward  and  downward  from  the 
inferior  colliculus  is  a  flat  ridge  formed  by  the  fibers  of  the 
lateral  lemniscus  (Herrick  ('18),  Fig.  45;  Cunningham  ('15), 
Fig.  517).  These  fibers  lie  dorsally  of  those  of  the  cerebral 
peduncle  and  superficially  of  those  of  the  brachium  con- 
junctivum;  at  the  upper  border  of  the  pons  they  turn  inward 
and  can  be  followed  downward  dorsally  of  the  deep  fibers  of  the 
pons  to  the  superior  olive.  This  small  nucleus  is  difficult 
to  identify,  since  its  cell  bodies  are  scattered  among  the  fibers, 
but  its  position  is  indicated  at  the  place  where  the  lemniscus 
fibers  turn  abruptly  medialward.  (Compare  the  next  para- 
graph for  the  relations  of  the  spinal  lemniscus  to  the  lateral 
lemniscus  and  Section  82  for  the  microscopic  appearance  of  this 
region.) 

107.  Having  traced  the  fibers  of  the  lateral  lemniscus  back- 
ward to  the  superior  olive,  the  ventral  spino-cerebellar  tract 
(of  Gowers)  and  the  spinal  lemniscus  (see  Section  105)  may  now 
be  traced  from  the  lower  border  of  the  pons  to  the  upper  bor- 
der of  the  superior  olive,  where  they  will  be  seen  to  accompany 
the  lateral  lemniscus  from  this  level  forward.     The  ventral 
spinocerebellar  tract  accompanies  the  lateral  lemniscus  com- 
plex into  the  midbrain,  where  its  fibers  may  be  seen  to  sepa- 
rate from  the  others  and  to  enter  the  cerebellum  by  the  way 
of  the  brachium  conjunctivum,  lying  more  superficially  than 
the  tract,  from  the  dentate  nucleus  to  the  red  nucleus. 

108.  The   medial    lemniscus. — Identify    again    the  nucleus 
of  the  fasciculus  gracilis  and  the  nucleus  of  the  fasciculus 
cuneatus.     These  receive  proprioceptive  fibers  from  the  spinal 
cord  by  way  of  the  fasciculus  gracilis  and  fasciculus  cuneatus. 
The  cell  bodies  of  these  nuclei  send  their  axones  to  the  thala- 
mus by  way  of  the  medial  lemniscus.     In  the  pons  region  this 
lemniscus  lies  ventrally  and  medially  of  the  superior  olive  and 
medially  of  the  lateral  lemniscus,  whose  fibers  it  adjoins  during 
their  course  through  the  upper  pons  and  midbrain  regions. 


98  LABORATORY    OUTLINE    OP   NEUROLOGY 

Identify  the  medial  lemniscus  in  the  region  of  the  superior 
olive.  It  will  be  found  as  a  broad  band  of  longitudinally 
directed  fibers  near  the  midplane  immediately  dorsally  of  the 
deepest  fibers  of  the  pons.  Tracing  them  downward  they  be- 
come crowded  into  the  space  between  the  two  inferior  olives. 
Under  the  nuclei  of  the  fasciculus  gracilis  and  fasciculus  cune- 
atus  these  fibers  cross  the  midplane  and  then  turn  abruptly 
dorsalward  in  numerous  strands  to  connect  with  these  nuclei 
of  the  opposite  side. 

In  the  dissection  of  the  medial  lemniscus  in  the  medulla  ob- 
longata  care  must  be  taken  not  to  destroy  the  pyramidal  tract 
which  lies  ventrally  of  it  and  the  fasciculus  longitudinalis 
medialis  and  tecto-spinal  tract  which  lie  dorsally  of  it. 

In  the  midbrain  the  medial  lemniscus  fibers  split  off  from 
those  of  the  lateral  lemniscus  shortly  before  the  latter  enter 
the  inferior  colliculus  and  the  medial  geniculate  body  (Herrick 
('18),  Fig.  75).  The  medial  lemniscus  continues  almost  di- 
rectly forward,  lying  ventrally  and  medially  of  the  lateral 
lemniscus,  and  ends  in  the  lateral  and  ventral  nuclei  of  the 
thalamus  (Herrick  ('18),  Figs.  77  and  78),  but  at  this  stage  of 
the  work  it  should  not  be  dissected  farther  forward  than  the 
midbrain. 

109.  The  fasciculus  longitudinalis   medialis. — In   the   me- 
dulla  oblongata  the   fibers  of  the  fasciculus   longitudinalis 
medialis  (posterior  longitudinal  bundle)  will  be  found  running 
close  to  the  median  plane  and  immediately  under  the  floor  of 
the  ventricle.     In  the  lower  parts  of  the  medulla  this  tract  lies 
dorsally  of  the  medial  lemniscus  and  separated  from  it  only  by 
the  tecto-spinal  tract,  but  in  the  pons  region  and  midbrain 
these  two  tracts  are  far  separated.     In  the  dissection  of  this 
tract  work  from  the  cut  median  surface  lateralward  and  do  not 
disturb  the  floor  of  the  fourth  ventricle  (cf.  Sections  92  and  93). 

110.  The  fasciculus  solitarius. — The  fasciculus  solitarius  can 
now  be  dissected  out.     Locate  again  the  ala  cinera  (trigonum 
vagi)  in  the  floor  of  the  fourth  ventricle.     This  marks  the  posi- 
tion of  the  dorsal  vagal  nuclei.     Tease  off  these  superficial  gray 
masses  and  expose  the  slender  fasciculus  solitarius  which  lies 
below  them.     Follow  this  tract  downward  and  upward  to  its 
ends  (cf.  Section  84). 


THE   MAMMALIAN   NERVOUS   SYSTEM  99 

111.  The  pyramidal  trad. — Now  complete  the  dissection  of 
the  pyramidal  tract  (tractus  cortico-spinalis)  from  the  pons 
downward  and  note  the  decussating  fibers  of  this  tract  on  the 
cut  median  surface  at  the  fower  end  of  the  oblongata.     These 
crossed  fibers  form  the  lateral  cortico-spinal  tract  of  the  cord. 
A  small  part  of  the  pyramidal  tract  does  not  decussate,  but 
descends  directly  and  forms  the  ventral  cortico-spinal  tract  of 
the  cord  (cf.  Sections  94  and  95). 

10.  The  Cerebrum 

112.  The  cerebrum  comprises  all  parts  of  the  brain  in  front  of 
the  isthmus.     It  is  further  subdivided  into  the  mesencephalon, 
diencephalon,  and  telencephalon.     Like  the  rhombencephalon, 
the  cerebrum  includes  a  stem  portion,  or  segment al  apparatus, 
and  a  suprasegmental  apparatus  (the  cerebral  cortex). 

The  brain  stem,  as  a  whole,  is  devoted  to  the  simpler  reflex 
and  instinctive  activities,  while  the  cerebral  cortex  serves  the 
higher  functions  of  association.  The  cerebral  hemispheres 
make  up  the  greater  part  of  the  telencephalon.  Each  cerebral 
hemisphere  comprises  cortical  and  basal  or  stem  portions. 
The  latter  includes  the  olfactory  bulb,  anterior  perforated 
space  (tuberculum  olfactorium),  septum,  corpus  striatum,  and 
some  other  parts.  The  cortex  (pallium)  has  two  great  sub- 
divisions, archipallium  (old  cortex)  and  neopallium  (new 
cortex).  The  archipallium  attains  its  maximum  development 
in  lower  mammals  and  is  chiefly  devoted  to  olfactory  correla- 
tions. It  comprises  the  hippocampus  and  part  of  the  gyrus 
hippocampi  (hippocampal  lobe  or  pyriform  lobe).  The  neo- 
pallium is  non-olfactory  cortex  and  attains  its  highest  devel- 
opment in  the  human  brain.  In  the  sheep  also  it  is  more 
extensive  than  the  archipallium,  occupying  the  convex  dorsal 
surface  of  the  hemisphere. 

113.  The  midbrain  and  thalamus. — On  the  medial  surfaces 
of  the  sheep  and  human  brains  review  the  aqueduct  of  Sylvius, 
the  boundaries  of  the  third  ventricle,  and  the  other  landmarks 
in  the  midbrain  and  thalamus  (see  Section  59) .     On  the  lateral 
aspect  of  the  specimens  locate  the  colliculus  inferior,  colliculus 
superior,    corpus   geniculatum   mediale,    corpus   geniculatum 
laterale  (medial,  or  internal,  and  lateral,  or  external,  geniculate 


100  LABORATORY    OUTLINE  OF   NEUROLOGY 

bodies),  and  the  pulvinar.  In  the  sheep  the  lateral  geniculate 
body  is  not  clearly  separate  from  the  pulvinar,  forming  the 
most  ventral  part  of  the  eminence  which  includes  both  of  these 
structures.  The  medial  geniculate  body  (Fig.  12)  is  con- 
nected with  the  inferior  colliculus  by  a  clearly  defined  ridge, 
the  peduncle  of  the  inferior  colliculus  (brachium  quadrigeminum 
inferius).  The  connection  of  the  lateral  lemniscus  with  the 
inferior  colliculus  and  medial  geniculate  body  has  already  been 
mentioned  (Sections  81,  82,  and  106).  The  optic  tract  is 
similarly  related  to  the  superior  colliculus,  lateral  geniculate 
body,  and  pulvinar  (Section  136) ;  but  the  further  dissection  of 
this  region  to  expose  these  connections  must  be  deferred  until 
after  the  removal  of  the  cerebral  hemisphere. 

114.  Examine  the  surface  of  the  human  cerebral  hemisphere 
and  locate  the  lobes  and  the  fissures  and  gyri  given  in  the  follow- 
ing list.  The  following  references  will  be  useful  in  identifying 
these  parts:  Cunningham  ('15),  Figs.  581,  582,  pp.  654,  655, 
Fig.  585,  p.  658,  Fig.  589,  p.  661;  Gray  ('18),  Figs.  724-728,  pp. 
817-821;  Herrick  ('18),  Figs.  52,  53,  54,  120;  Morris  ('14),  Figs. 
675-679;  Piersol  ('16),  Figs.  984-993,  pp.  1138-1152;  Quain 
('09),  Vol.  Ill,  Pt.  1,  Figs.  255-259,  pp.  255-259;  Rauber- 
Kopsch  ('12),  Figs.  91,  92,  95,  96,  pp.  71-78;  Sobotta  ('11), 
Figs.  623-634;  Spalteholz  ('09),  Figs.  705-714,  pp.  637-644; 
Toldt  ('04),  Figs.  1191-1197,  pp.  775-779. 

lobus  frontalis,  lobus  parietalis,  lobus  occipitalis,  lobus  tem- 

poralis,  insula  (island  of  Reil) 
fissura  cerebri  lateralis  (Sylvii) 

sulcus  centralis  (fissure  of  Rolando)  and  sulcus  precentralis 
sulci  temporalis  superior,  medius,  and  inferior 
fissura  calcarina  and  cuneus 
sulcus  cinguli  and  gyrus  cinguli 
fissura  collateralis 

gyri  frontalis  superior,  medius,  and  inferior 
operculum  insulse  (temporal,  parietal,  frontal,  and  orbital  parts) 
"Broca's  convolution"  (the  opercular  part  of  the  left  gyrus 

frontalis  inferior) 

gyrus  centralis  anterior  (precentral  gyrus) 
gyrus  centralis  posterior  (postcentral  gyrus) 


THE   MAMMALIAN   NERVOUS   SYSTEM  101 

gyri  temporalis  superior,  medius,  and  inferior 
gyrus  hippocampi  and  uncus,  fissura  hippocampi 

115.  The  cerebral  hemisphere  of  the  sheep. — Note  the  ar- 
rangement of  gyri  and  sulci  in  the  cerebral  hemisphere  of  the 
sheep  and  locate  the  motor  area  of  the  cortex  (see  Fig.  9, 
Simpson  and  King   ('11),   and  King   ('11)).     Compare  this 
arrangement  with  that  of  the  human  brain  and  note  the 
differences.     On  the  comparative  anatomy  of  the  sulci,  see 
Rappers  ('13). 

116.  Cortical  localization. — With  the  aid  of  the   gyri  and 
sulci  just  listed  locate  each  of  the  projection  centers  and  as- 
sociation areas  on  your  specimen.     The  following  references 
may  be  consulted:  Barker  ('01),  Fig.  657,  p.  1037;  Barker  ('16), 
Fig.  588,  p.  436;  Cunningham  ('15),  Fig.  588,  p.  660,  Fig.  591, 
p.  663,  also  see  references  under  Section  114;  Gushing  ('08)  and 
('09);  Edinger  ('93) ;  Edinger  and  Fischer  ('13);  Flechsig  ('96); 
Gray  ('18),  Figs.  756,  757;  Herrick  ('18),  Figs.  130,  131,  135, 
136;  Horsley  ('09);  Howell  ('18),  Figs.  86-88,  pp.  195-197, 
Fig.  97,  p.  222,  Figs.  98-101,  pp.  227,  228,  also  discussions  in 
Chap.  IX,  pp.  192-201,  and  Chap.  X;  Leyton  and  Sherring- 
ton  ('17);  Monakow  ('14);  Morris  ('14),  Fig.  703,  p.   892, 
Fig.  704,  p.  894;  Rauber-Kopsch  ('12),  Figs.  250,  251,  pp.  253, 
254;  Starling  ('15), 'pp.  434-457;  Stewart  ('18),  pp.  947-975; 
Villiger  ('12),  Figs.  118-122,  and  discussion  pp.  123-130. 

117.  Gross  structure  of  the  cerebral  cortex. — Remove  a  small 
rectangular  block  containing  about  one  square  centimeter  of 
cortex  from  each  of  the  following  centers  of  the  human  cerebral 
cortex:  visual,  auditory,  tactile,  motor,  prefrontal.     Cut  each 
block  so  as  to  exhibit  a  section  through  the  cortex  strictly 
perpendicular  to  the  surface  and  observe  with  a  lens  the  details 
of  the  lamination  of  the  gray  and  white  substance  within  the 
cortex.     These  distinctions  are  visible  only  in  well-preserved 
material;  cf.  Cunningham  ('15),  pp.  644-647;  Herrick  ('18), 
Fig.  122;  Quain  ('09),  Vol.  Ill,  Pt.  I,  pp.  372,  373;  and  Elliot 
Smith  ('07). 

118.  Microscopic  structure  of  the  cerebral  cortex. — Study  the 
microscopic  sections  of  the  cerebral  cortex  supplied  and  note 
particularly  the  differences  in  the  lamination  of  the  cells  and 


102  LABORATORY    OUTLINE    OF   NEUROLOGY 

fibers  in  the  different  regions.  See  Bailey  ('16),  pp.  542-549; 
Barker  ('01),  Figs.  655,  656,  pp.  1034,.  1035;  Bolton  and  Moyes 
('12);  Brodmann  ('07);  Campbell  ('05);  Cunningham  ('15), 
Fig.  574,  p.  645,  and  also  the  references  under  Sections  114  and 
115;  Herrick  ('18),  Chap.  XIX;  Rauber-Kopsch  ('12),  pp. 
175-186;  ViUiger  ('12),  pp.  114-118. 

119.  Association  tracts  of  the  sheep. — Now  in  the  sheep's 
brain  by  careful  teasing  examine  the  arrangement  of  fibers  in 
the  subcortical  white  matter.  Only  a  part  of  these  fibers  are 
to  be  studied  at  this  time,  and  the  dissection  outlined  in  this 
section  should  not  be  carried  farther. than  directed.  It  will 
require  but  a  short  time. 

(1)  First,  along  the  dorsal  border  of  the  medial  surface  of 
the  hemisphere  scrape  away  the  gray  matter  covering  two  ad- 
jacent gyri.     This  will  bring  into  view  the  short  associational 
(arcuate)  fibers  connecting  these  gyri.     Further  teasing  will 
show  that  similar  fibers,  lying  deeper  in  the  white  matter,  con- 
nect more  remote  gyri. 

(2)  Careful  dissection  of  the  lateral  surface  of  the  hemi- 
sphere will  show  that  from  other  association  areas  of  the  cere- 
bral cortex  fibers  sweep  down  into  the  pyriform  (hippocampal) 
lobe,  indicating  the  linking-up  of  all  association  areas  of  the 
neopallium  with  the  association  areas  of  the  archipallium.  . 

(3)  The  cingulum  is  a  long  associational  tract  running  close 
to  the  cortex  of  the  medial  surface  of  the  hemisphere.     In  part 
of  its  course  it  runs  parallel  with  the  dorsal  surface  of  the  corpus 
callosum.     It  begins  anteriorly  in  the  gyrus  subcallosus  under 
the  rostrum  of  the  corpus  callosum,  arches  upward  at  the  genu 
of  the  corpus  callosum,  and  at  its  posterior  end  passes  around 
the  splenium  of  the  callosum  and  then  goes  downward,  for- 
ward, and  lateralward  to  the  region  of  the  hippocampal  gyrus. 
Begin  its  dissection  above  the  callosum  and  follow  it  in  both 
directions  to  its  termini. 

(4)  The  corpus  callosum. — These  fibers  connect  all  parts  of 
the  neopallium  of  one  hemisphere  with  those  of  the  opposite 
hemisphere.     Break  through  the  middle  of  the  cingulum  and 
tease  out  a  small  part  of  the  callosal  fibers  to  their  connection 
with  the  cortex.     Do  not  disturb  the  remainder  of  the  callosum 
at  this  time. 


THE    MAMMALIAN    NERVOUS    SYSTEM  103 

(5)  The  corona  radiata. — This  name  is  given  to  those  fibers 
which  run  between  the  cortex  and  the  underlying  parts  of  the 
brain  stem.  Most  of  them  run  through  the  internal  capsule  of 
the  corpus  striatum  (see  Sections  138,  139,  144,  145,  and  Her- 
rick  ('18),  Figs.  77,  79,  80).  They  include  the  projection  fibers 
of  the  great  sensory  systems  from  the  thalamus,  various 
other  thalamo-cortical  connections,  the  voluntary  motor  corti- 
cal tracts  (including  the  pyramidal  and  cortico-bulbar  tracts), 
and  the  cortico-pontile  tracts.  These  fibers  are  named  from 
the  fact  that  they  diverge  from  the  upper  border  of  the  internal 
capsule  like  the  rays  of  a  crown.  In  the  dissection  at  this  stage 
the  broken  ends  of  the  vertical  corona  radiata  fibers  are  seen 
breaking  through  the  transverse  sheet  of  callosal  fibers  which 
run  at  right  angles  to  them.  The  cingulum  and  other  longitud- 
inal association  tracts  of  the  hemisphere  run  at  right  anglef  to 
both  of  these  systems 

120.  Association  tracts  of  the  human  brain. — In  the  human 
brain  tease  away  the  tissues  on  the  dorsal  and  lateral  walls  of 
the  hemisphere  and  dissect  out: 

(1)  short  association  fibers 

(2)  fasciculus  longitudinalis  superior 

(3)  fasciculus  occipito-frontalis  inferior 

(4)  fasciculus  uncinatus 

(5)  fasciculus  transversus  occipitalis 

(6)  fasciculus  longitudinalis  inferior 

(7)  the  cingulum 

These  represent  a  few  only  of  the  more  clearly  defined  asso- 
ciation bundles,  of  which  the  white  matter  of  the  hemispheres 
is  largely  made  up.  While  making  these  dissections  note 
the  relations  of  the  fibers  of  the  corpus  callosum  and  of  the 
corona  radiata.  In  well-preserved  brains  these  tracts  can  be 
dissected  out  with  great  completeness  (see  Section  141).  Even 
in  poorly  preserved  brains  some  of  them  can  usually  be  demon- 
strated. See:  Barker  ('01),  Chap.  LXVII,  pp.  1058-1069; 
Cunningham  ('15),  Figs.  577,  578,  pp.  649,  650;  Curran  ('09); 
Gray  ('18),  Fig.  751;  Herrick  ('18),  Fig.  121;  Howell  ('15), 
Fig.  83,  p.  185;  Morris  ('14),  Figs.  701,  702,  p.  891;  Quain  ('09), 
Vol.  Ill,  Pt.  I,  Fig.  323,  p.  359;  Toldt  ('04),  Figs.  1230,  1231; 
Villiger  ('12),  Figs.  124-127,  p.  134. 


104  LABORATORY   OUTLINE    OF  NEUROLOGY 

121.  Rhinencephalon. — The  entire  olfactory  part  of  the  brain 
is  called  the  rhinencephalon.     This  apparatus  is  so  much  more 
highly  developed  in  the  sheep  than  in  man  that  the  dissection 
is  much  more  readily  carried  out  upon  this  brain.     Before 
undertaking  the  following  dissection  look  up  in  the  reference 
books  the  structure  of  the  olfactory  epithelium,  nerve  and  bulb. 
See  Cunningham   (15),  p.   623;  Herrick   ('18),   Chap.   XV; 
Howell  ('18),  pp.  299-305;  Villiger  ('12),  Fig.  116,  p.  118. 
On  the  nervus  terminalis  see  Section  47  (d). 

The  peripheral  olfactory  neurons  arise  from  cells  lying  in 
the  mucous  membrane  of  the  nose.  These  fibers  terminate  in 
the  olfactory  bulb,  which  is  the  primary  olfactory  center  of  the 
brain.  Here  lie  the  neurons  of  the  second  order  (mitral  cells), 
whose  axons  constitute  the  olfactory  tracts,  or  striae,  terminat- 
ing in  secondary  olfactory  centers  in  the  basal  parts  of  the 
cerebral  hemisphere. 

These  secondary  centers  in  the  aggregate  are  called  the  area 
olfactoria  and  the  fibers  of  the  second  order  terminating  in 
them  are  called  tractus  olfactorius  (lateralis,  medialis,  and  in- 
termedius).  The  tracts  of  the  third  order  are  usually  named 
by  hyphenated  compound  words,  of  which  the  second  member 
designates  the  center  into  which  the  tract  discharges,  thus  we 
have  the  tractus  olfacto-habenularis,  tractus  olfacto-mamil- 
laris,  tractus  olfacto-corticalis,  etc.  The  tertiary  olfactory 
centers  into  which  these  tracts  of  the  third  order  discharge 
are  arranged  in  two  series:  (1)  the  basal  centers  of  the  dien- 
cephalon  and  cerebral  peduncle  for  olfactory  reflexes,  and  (2) 
the  cortical  centers  in  the  hippocampus  and  gyms  hippocampi. 

122.  Peripheral  olfactory  organ. — If  microscopic  sections  of 
the  nasal  epithelium  are  available,  they  should  be  studied  at 
this  time.     Note  that  this  sensory  epithelium  differs  histologic- 
ally  in  important  respects  from  any  other  in  the  human  body. 
See  Barker  ('01),  Fig.  208;  Herrick  ('18),  Figs.  36, 103,  and  104; 
Piersol  (16),  Figs.  1179,  1180,  p.  1415;  Quain  (;09),  Figs.  70 
and  71. 

123.  Olfactory  tracts  of  the  sheep. — The  olfactory  fibers  of 
the  second  order  arise  from  the  mitral  cells  of  the  olfactory  bulb 
and  form  the  tractus  olfactorius,  of  which  there  are  three 
parts.     For  their  arrangement  in  the  sheep  see  Fig.  8. 


THE    MAMMALIAN    NERVOUS    SYSTEM  105 

(1)  Stria   olfactoria  lateralis    (radix   lateralis   bulbi    olfac- 
torii). — This  can  easily  be  dissected  out,  following  the  fissura 
rhinalis  from  the  olfactory  bulb  to  the  tip  of  the  gyrus  hippo- 
campi (lobus  hippocampi,  lobus  piriformis).     In  the  human 
brain  it  runs  farther  lateralward  in  the  lateral  fissure  to  the 
border  of  the  insula  and  then  bends  sharply  medialward  and 
backward  to  enter  the  uncus  of  the  temporal  lobe. 

(2)  Stria   olfactoria   medialis    (radix  medialis  bulbi  olfac- 
torii) . — This  can  be  dissected  out  and  will  be  found  to  ascend 
on  the  median  surface  of  the  hemisphere  and  to  terminate 
chiefly  in  the  medial  olfactory  area  under  the  genu  of  the  corpus 
callosum.     This   area   includes   the    gyrus    subcallosus    and 
septum. 

(3)  Stria  olfactoria  intermedia. — This  lies  between  the  me- 
dial and  lateral  striae.     Part  of  it  can  be  dissected  out  directly 
into  the  anterior  commissure  (Burkholder  ('12),  Plate  XIX), 
within  which  it  decussates  to  terminate  in  the  anterior  perfor- 
ated space  (tuberculum  olfactorium)  of  the  opposite   hemi- 
sphere.    This  tract  can  best  be  dissected  by  locating  the 
anterior  commissure  on  the  median  surface  of  the  specimen  and 
then  teasing  its  fibers  out  as  they  pass  lateralward  and  forward 
toward  the  olfactory  bulb.     (The  anterioj  commissure  contains 
other  fibers  besides  these,  some  of  which  pass  between  the 
corpora  striata  of  the  two  hemispheres  and  others  enter  the 
stria  terminalis;  see  Sections  125  (5)  and  132.)     A  second  part 
of  the  stria  olfactoria  intermedia,  composed  of  more  scattered 
fibers,  terminates  in  the  region  of  the  anterior  perforated  space 
of  the  same  side. 

124.  The  area  olfactoria. — This  area  includes  the  terminal 
nuclei  of  the  olfactory  tracts  mentioned  in  the  preceding 
section. 

The  area  olfactoria  lateralis  includes  the  gray  matter  accom- 
panying the  lateral  olfactory  tract,  or  the  lateral  olfactory 
nucleus  (termed  by  Retzius  in  the  human  embryo,  lateral 
olfactory  gyrus;  see  Herrick  ('18),  Fig.  105),  and  the  part  of  the 
temporal  lobe  reached  by  the  lateral  olfactory  tract  (region  of 
the  uncus)  and  the  amygdala.  Cf.  Section  126  (3). 

The  area  olfactoria  medialis  includes  the  gyrus  subcallosus 
(pedunculus  corporis  callosi),  area  parolfactoria  of  Broca  and 


106  LABORATORY   OUTLINE    OF   NEUROLOGY 

septum.  See'Herrick  ('18),  Fig.  52.  It  is  reached  by  the 
medial  olfactory  tract. 

The  area  olfactoria  intermedia  lies  between  the  two  areas  last 
mentioned  and  includes  the  anterior  perforated  space  (in  lower 
mammals  the  tuberculum  olfactorium).  It  is  reached  by  the 
intermediate  olfactory  tract,  part  of  these  fibers  first  decussat- 
ing in  the  anterior  commissure. 

Tracts  of  the  third  order  arise  from  all  parts  of  the  olfactory 
area,  and  these  will  be  considered  under  two  heads:  (1)  the 
reflex  tracts,  and  (2)  the  cortical  tracts. 

125.  Reflex  olfactory  tracts. — These  pass  from  the  olfactory 
area  to  the  brain  stem  centers  in  the  amygdala,  diencephalon, 
and  cerebral  peduncle.  Most  of  them  can  be  dissected  in  the 
brain  of  the  sheep.  See  Herrick  ('18),  Fig.  106. 

(1)  Tractus  olfacto-mamillaris. — This  is  a  diffuse  collection 
of  fibers  from  the  medial  and  intermediate  olfactory  areas 
passing  backward  dorsally  of  the  optic  chiasma  to  enter  the 
corpus  mamillare.     It  can  be  dissected,  though  with  some  dif- 
ficulty on  account  of  the  scattered  arrangement  of  its  fibers. 

(2)  Tractus    olfacto-habenularis.  —  Fibers    originating    with 
those  last  described  can  be  seen  in  a  careful  dissection  to 
separate  from  them  below  the  interventricular  foramen  and 
then  to  turn  dorsalward  immediately  behind  the  foramen. 
They  enter  the  stria  medullaris  thalami,  a  strong  superficial 
fiber  tract  passing  across  the  rostral  border  of  the  thalamus  and 
bordering  the  tsenia  thalami.     This  tract  is  sometimes  called 
the  tractus  tsenise;  it  terminates  in  the  habenula. 

(3)  Tracing  olfacto-tegmentalis. — These  fibers  originate  with 
those  of  the  tractus  olfacto-mamillaris,  but  instead  of  terminat- 
ing in  the  mammillary  body  they  pass  on  to  enter  the  tegmen- 
tum  of  the  cerebral  peduncle.     They  can  be  dissected,  though 
they  are  hard  to  separate  from  tractus  olfacto-mamillaris. 

(4)  The  olfactory  projection  tract  of  Cajal  passes  from  the 
lateral  olfactory  area  and  amygdala  backward  into  the  regions 
of  the  mammillary  body  and  cerebral  peduncle.     We  have  not 
been  able  to  dissect  these  fibers,  but  they  can  be  demonstrated 
microscopically. 

(5)  Stria  terminalis. — This  tract  (also  called  stria  or  taenia 
semicircularis)  connects  the  medial  olfactory  area  in  the  vicin- 


THE   MAMMALIAN   NERVOUS   SYSTEM  107 

ity  of  the  anterior  commissure  with  the  amygdala  under  the 
uncus,  running  dorsally  of  the  internal  capsule  fibers  at  the  line 
of  contact  of  the  thalamus  with  the  cerebral  hemisphere.  The 
dissection  of  this  tract  should  not  be  made  at  this  time;  see 
Section  132. 

(6)  Diagonal   band   of  Broca. — This  is  a  ridge  extending 
transversely  across  the  ventral  aspect  of  the  cerebral  hemi- 
sphere between  the  area  olfactoria  intermedia,  or  tuberculum 
olfactorium,  and  the  optic  chiasma  (Fig:  8).     It  contains  both 
cells  and  fibers,  the  latter  connecting  the  medial  olfactory  area 
with  the  lateral  olfactory  area.     The  diagonal  band  and  the 
stria  terminalis  contain  correlation  fibers  connecting  the  same 
areas,  the  former  running  across  the  extreme  ventral  surface  of 
the  hemisphere  and  the  latter  across  the  extreme  dorsal  surface 
of  the  brain  stem  along  the  line  of  contact  of  the  cerebral 
hemisphere  with  the  thalamus. 

(7)  Tractus   mamillo-thalamicus   (tract  of  Vicq  d'Azyr  or 
tractus  thalamo-nlamillaris) . — This  tract  runs  from  the  cor- 
pus mamillare  forward  and  dorsalward  to  the  nucleus  ante- 
rior of  the  thalamus.     It  can  readily  be  dissected  by  scraping  off 
the  ependyma  of  the  third  ventricle,  beginning  in  the  region  of 
the  mammillary  body. 

(8)  Tractus  mamillo-tegmentalis. — By  very  slight  dissection, 
beginning  in  the  median  plane,  this  tract  can  be  exposed.     It 
runs  from  the  mammillary  body  dorsalward  and  spinalward 
through  the  tegmental  region  under  the  aqueduct  of  Sylvius. 

(9)  Tractus  mamillo-peduncularis. — This  tract  arises  with 
the  last  and  runs  somewhat  farther  ventrally  in  the  cerebral 
peduncle. 

(10)  Tractus  habenulo-peduncularis   (fasciculus  retroflexus, 
or  Meynert's  bundle) .     This  tract  also  can  readily  be  dissected. 
It  runs  from  the  habenula  into  the  ventral  part  of  the  cerebral 
peduncle  immediately  behind  the  mammillary  body,  crossing 
the  tractus  mamillo-tegmentalis  at  a  somewhat  deeper  level 
(more  laterally). 

The  three  tracts  last  mentioned  carry  olfactory  nervous 
impulses  into  the  motor  centers  of  the  cerebral  peduncle. 
After  synapses  here  the  pathways  are  continued  to  the  lower 
motor  centers. 


108  LABORATORY    OUTLINE    OF   NEUROLOGY 

126.  Cortical  olfactory  tracts. — All  parts  of  the  olfactory  area 
discharge  tracts  of  the  third  order  into  the  cerebral  cortex 
(hippocampus  and  gyrus  hippocampi). 

(1)  Tractus  olfacto-corticalis  medialis. — These  fibers  ascend 
from  the  medial  and  intermediate  olfactory  areas  close  to  the 
median  plane  between  the  corpus  callosum  and  the  anterior 
commissure  to  enter  the  body  of  the  fornix  and  fimbria.     They 
are  drawn,  but  not  named,  in  the  region  marked  S  in  Fig.  106  of 
Herrick  ('18).     They  pass  through  the  fimbria  to  terminate  in 
the  hippocampus  (see  Section  127). 

(2)  Stria  longitudinalis  medi alis  (" nerve"  of  Lancisius).     A 
few  fibers  belonging  to  the  same  system  as  the  last  pass  dorsally 
instead  of  ventrally  of  the  corpus  callosum.     By  exposing  the 
dorsal  surface  of  the  callosum  they  can  be  seen  curving  around 
the  genu,  passing  backward  along  its  dorsal  surface  close  to  the 
median  plane,  then  curving  ventrally  around  the  splenium  to 
enter   the   underlying   hippocampus    (see   Burkholder    ('12), 
Plates  XI  and  XII).     These  fibers  are  accompanied  by  the 
thin  gray  "indusium  verum,"  which  is  a  vestige  of  an  extension 
of  the  hippocampus  above  the  callosum  which  is  found  in  the 
lowest  mammals.     See  Herrick   ('18),  Fig.   106,  h.  sc.,  and 
Johnston  ('06),  Chap.  XVIII.     These  structures  are  smaller  in 
man  than  in  the  sheep,  though  they  may  still  be  recognized. 
See  Cunningham  ('15),  Fig.  554,  p.  626;  Morris  ('14),  Fig.  672, 
p.  852;  Spalteholz  ('09),  Fig.  715;  Toldt  ('04),  Fig.  1198,  p.  780; 
Villiger  ('12),  Figs.  32-34,  36,  39. 

(3)  Tractus   olfacto-corticalis   lateralis. — These   fibers  arise 
from  the  lateral  olfactory  nucleus  and  enter  the  ventrolateral 
end  of  the  hippocampus  in  the  uncus  region  of  the  temporal 
lobe.     They  accompany  those  of  the  lateral  olfactory  tract. 

The  uncus  and  adjacent  parts  of  the  temporal  lobe  are  of 
transitional  type.  Forward  they  merge  into  the  lateral  olfac- 
tory nucleus,  laterally  into  the  neopallium  (see  Section  112) 
through  the  gyrus  hippocampi,  and  medially  into  the  archipal- 
lium  through  the  hippocampus  (see  Section  127). 

127.  The  hippocampus  and  fornix. — When  the  relations  of 
the  olfactory  tracts  of  the  sheep  already  described  are  clearly 
in  mind,  remove  the  septum  pellucidum  and  look  into  the 
lateral  ventricle,  drawing  apart  the  corpus  callosum  and  the 


THE   MAMMALIAN   NERVOUS    SYSTEM  109 

underlying  corpus  fornicis  (see  Fig.  10).  Locate  the  hippo- 
campus in  the  floor  of  the  posterior  horn  of  the  lateral  ventricle; 
also  the  fimbria  and  hippocampal  commissure  (the  latter  lying 
in  the  corpus  fornicis  and  connecting  the  hippocampi  of  the 
two  hemispheres).  Now  cut  through  the  splenium  of  the  cor- 
pus callosum,  separating  the  parts  last  mentioned  from  the 
overlying  corpus  callosum.  Working  carefully  continue  this 
cut  laterally  and  ventrally;  cutting  from  the  ventricular  wall 
back  into  the  lobus  hippocampi  and  general  cortex  along  the 
posterior  and  outer  border  of  the  hippocampus  for  its  entire 
length  downward  to  the  tip  of  the  gyrus  hippocampi.  Now 
beginning  in  the  gyrus  hippocampi  (into  which  the  lateral 
olfactory  tract  has  already  been  traced),  note  carefully  the 
shape  and  position  of  the  hippocampus  and  its  fiber  tract,  the 
fimbria,  as  you  pass  toward  the  midline. 

The  hippocampus  is  the  chief  part  of  the  archipallium,  or 
olfactory  cerebral  cortex.  It  is  a  buried  convolution  rolled 
into  the  lateral  ventricle  from  the  ventral  and  occipital  margins 
,of  the  cortex  cerebri  along  the  fissure  hippocampi.  It  is  en- 
tirely covered  by  the  gyrus  hippocampi  with  which  its  tissue  is 
confluent.  On  its  ventral  side  is  a  subsidiary  convolution,  the 
gyrus  dentatus  (fascia  dentata),  and  it  gives  rise  to  a  sheet  of 
fibers,  the  fimbria,  which  passes  forward  in  the  floor  of  the 
lateral  ventricle  to  enter  the  body  of  the  fornix  (corpus  fornicis, 
an  unpaired  mass  of  fibers  under  the  splenium  of  the  corpus 
callosum).  Here  some  of  the  fibers  cross  to  the  other  side 
forming  the  commissura  hippocampi,  the  entire  complex  form- 
ing the  lyra.  Others  descend  into  the  diencephalon  as  the 
columna  fornicis  (Section  129). 

128.  The  hippocampus. — Make  a  cross-section  through  the 
hippocampus  and  lobus  hippocampi  and  draw  the  cross-section, 
showing  the  relation  of  the  fimbria,  hippocampus,  and  gyrus 
dentatus.     Note  that  this  section  is  not  transverse  to  the 
whole  hemisphere  in  this  region,  but  only  to  the  hippocampal 
formation. 

129.  Column  of  the  fornix — Now  from  the  body  of  the  fornix 
follow  the  column  of  the  fornix  (columna  fornicis),  dissecting 
it  out  as  you  go,  forward  to  a  position  just  above  the  anterior 
commissure  and  then  backward  and  ventrally  to  the  mammil- 


110  LABOKATORY    OUTLINE    OP    NEUROLOGY 

lary  body  (see  Burkholder  ('12),  Plate  XX) .  A  small  part  may 
be  seen  to  turn  back  immediately  behind  the  interventricular 
foramen  to  enter  the  stria  medullaris  and  so  reach  the  habenula. 
The  column  of  the  fornix  consists  mainly  of  fibers  passing  out 
of  the  hippocampus  by  way  of  the  fimbria  into  the  olfactory 
correlation  centers  of  the  hypothalamus  and  epithalamus. 

The  column  of  the  fornix  is  the  efferent  projection  tract  from 
the  olfactory  cortical  center  (hippocampus)  to  the  mammillary 
body  and  habenula;  that  is,  it  carries  motor  impulses  from  the 
olfactory  cortex  to  the  diencephalic  olfactory  centers.  From 
these  latter  centers  these  impulses  are  carried  by  the  same 
tracts  as  those  from  the  subcortical  reflex  centers;  see  Section 
125  (7)  to  (10). 

130.  The  following  references  to  figures  of  the  human  brain 
will  aid  in  understanding  the  relations  of  the  olfactory  ap- 
paratus of  the  sheep:  Barker  ('01),  Chap.  LII;  Cunningham 
('15),  pp.  623-628,  also  Fig.  566,  p.  637;  Gray  ('18),  Figs.  732, 
747,  748;  Herrick  ('18),  Chap.  XV;  Morris  ('14),  Fig.  690,  p. 
877,  also  pp.  864-873;  Piersol  ('16),  Figs.  1018,  1019,  pp.  1180, 
1181,  Figs.  998-1000,  pp.  1158-1161,  Fig.  1002,  p.  1163,  Figs. 
1004-1006,  pp.  1165-1167;  Sobotta  ('11),  Figs.  634-641. 

Master  now,  by  the  aid  of  text-books  and  diagrams,  the  ol- 
factory system  and  its  connections  and  relations  as  seen  in  the 
sheep  which  is  the  same  in  plan  as  in  the  human  brain.  Re- 
view the  entire  dissection,  tracing  the  course  of  olfactory  im- 
pulses through  the  reflex  pathways  and  centers  of  the  basal 
regions  from  the  nose  to  the  epithalamus  and  hypothalamus 
and  through  the  cortical  pathways  to  the  hippocampus  and 
thence  again  to  the  epithalamus  and  hypothalamus.  This 
gives  a  schematic  picture  of  the  workings  of  the  entire  rhinen- 
cephalon.  This  should  be  done  before  further  work  is  under- 
taken and  an  analysis  of  these  pathways  fully  written  up. 

131.  Now  cut  through  the  genu  of  the  corpus  callosum  for- 
ward and  downward  toward  the  olfactory  bulb,  thus  opening 
up  the  anterior  horn  of  the  lateral  ventricle,  which  in  the  sheep 
is  directly  continuous  with  the  ventricle  of  the  olfactory  bulb. 
(In  the  human  brain  the  ventricle  of  the  olfactory  bulb  is 
obliterated  in  the  adult.) 

132.  Beginning  now  in  the  gyrus  hippocampi  at  the  most 


THE   MAMMALIAN   NERVOUS   SYSTEM  111 

lateral  border  of  the  lateral  ventricle,  note  the  positions  of  the 
stria  terminalis  (stria  or  tsenia  semicircularis),  plexus  chorioi- 
deus  of  the  lateral  ventricle  and  tail  of  the  caudate  nucleus. 
Follow  the  last  three  medially  and  anteriorly,  noting  carefully 
their  relationships  to  each  other  and  to  the  hippocampus,  until 
the  anterior  end  of  the  head  of  the  caudate  nucleus  is  reached 
near  the  region  of  the  anterior  perforated  space.  The  stria  ter- 
minalis can  be  traced  forward  into  the  anterior  commissure. 
Tracing  the  stria  terminalis  backward  into  the  temporal  lobe 
it  will  be  seen  to  enter  the  anterior  tip  of  the  gyrus  hippocampi, 
where  it  ends  in  a  small  deep  gray  mass,  the  nucleus  amygdalce. 
See  Cunningham  ('15),  Figs.  539,  563;  Herrick  ('18),  Figs.  76 
and  121;  Morris  ('14),  Figs.  658,  688,  691,  pp.  834,  875,  878 
respectively;  Piersol  ('16),  see  references  under  Section  130; 
Quain  ('09),  Vol.  Ill,  Pt.  1,  Figs.  228,  233,  294,  pp.  224,  229, 
294  respectively. 

133.  Draw  the  dissection  at  this  stage,  as  seen  from  above, 
showing  the  form  of  the  lateral  ventricle  and  the  structures 
which  form  its  walls  (cf.  Burkholder  ('12),  Plates  XIII-XVI). 

134.  Now  pulling  carefully  so  as  to  tear  the  tissue  slightly, 
draw  away  the  ventricular  wall  along  the  upper  border  of  the 
caudate  nucleus.     The  internal  capsule  fibers  can  now  be  seen 
passing  downward  and  backward,  lateral  to  the  caudate  nu- 
cleus.    By  teasing  away  the  remaining  association  fibers  on  the 
lateral  side  of  the  hemisphere  the  lentiform  nucleus  (a  large 
gray  mass)  will  be  exposed  to  view  and  the  internal  capsule 
fibers  will  be  seen  passing  downward  and  posteriorly  between 
the  caudate  and  lentiform  nuclei.     By  teasing  away  the  gray 
cell  masses  of  the  lentiform  nucleus  some  of  the  fiber  bundles 
can  be  seen  passing  into  the  cerebral  peduncle  (pedunculus 
cerebri).     Care  must  be  taken  not  to  dissect  too  deeply  and 
thus  injure  the  underlying  thalamus,  which  lies  medially  of  the 
posterior  part  of  the  internal  capsule  (cf.  Burkholder  ('12), 
Plate  XXII). 

135.  Retina. — If   microscopic    preparations   are    available, 
study  the  histological  structure  of  the  retina.     From  the  refer- 
ence books  master  the  arrangements  of  its  neurons  and  the 
course  of  nervous  impulses  within  it.     See  Bailey  ('16),  pp. 
561-565;  Barker  ('01),  Chap.  XXXVII,  pp.  532-543;  Cunning- 


112  LABORATORY   OUTLINE    OF   NEUROLOGY 

ham  ('15),  pp.  814-818;  Herrick  ('18),  Figs.  97-99;  Howell 
('18),  Chap.  XVIII.  On  the  general  structure  of  the  eye,  see 
Section  14. 

136.  Optic  system. — In  the  sheep  dissection  remove  the  hip- 
pocampus.    Identify  the  structures  on  the  lateral  surface  of 
the   thalamus   and   midbrain:   pulvinar,   lateral   and   medial 
geniculate  bodies,  superior  and  inferior  colliculi.     Follow  the 
optic. tract  from  the  chiasma  to  the  thalamic  optic  centers 
(pulvinar  and  lateral  geniculate  body),  where  the  thalamic 
optic  fibers  terminate.     Trace  other  fibers  of  the  optic  tract 
over  the  surface  of  the  medial  geniculate  body  to  the  superior 
colliculus  of  the  midbrain  (optic  tectum).     This  is  the  center 
for  the  optic  reflexes  of  accommodation,  etc. 

By  teasing  away  the  gray  matter  of  the  pulvinar,  optic  pro- 
jection fibers  can  be  followed  from  the  pulvinar  to  the  occipital 
pole  of  the  cerebral  hemisphere.  The  pulvinar  and  lateral 
geniculate  body  are  the  thalamic  centers,  which,  through  their 
connections  with  the  cerebral  cortex,  provide  for  conscious 
visual  responses.  See  Bailey  ('16),  Fig.  358,  p.  534;  Cunning- 
ham ('15),  pp.  619,  620;  Edinger  ('11),  Fig.  220,  p.  296;  Gray 
('18),  Figs.  773,  774,  pp.  882,  883;  Herrick  ('18),  Chap.  XIV; 
Morris  ('14),  Figs.  655-660,  pp.  844,  845,  Fig.  670,  p.  849; 
Piersol  ('16),  pp.  1223-1225;  Quain  ('09),  Vol.  Ill,  Pt.  I,  Figs. 
232,  233,  pp.  228,  229,  Fig.  243,  p.  240;  Rauber-Kopsch  ('12), 
Figs.  109,  111,  112,  123,  124,  261;  Villiger  ('12),  pp.  172-174. 

137.  Auditory  system. — The  medial  geniculate  body  of  the 
sheep  (thalamic  auditory  center)  and  the  inferior  colliculus 
(midbrain  auditory  center)  should  again  be  located  (Fig.  12), 
also  the  arm  of  the  inferior  colliculus  (brachium  quadrigem- 
inum  inf erius) ,  which  is  the  auditory  path  between  the  inferior 
colliculus  and  the  medial  geniculate  body. 

Auditory  projection  fibers  pass  from  the  medial  geniculate 
body  through  the  internal  capsule  to  the  temporal  lobe  of  the 
cerebral  cortex,  but  these  cannot  well  be  separated  by  dissec- 
tion in  the  sheep. 

138.  Dissection  of  the  pyramidal  tract. — As  the  last  step  of 
the  sheep  dissection,  by  careful  tearing  down  of  the  fibers  follow 
out  some  of  the  internal  capsule  fibers  into  the  regions  of  the 
thalamus,  midbrain,  and  medulla  oblongata.     Try  especially 


THE    MAMMALIAN   NEKVOTJS    SYSTEM  113 

to  work  out  the  cortico-spinal  (pyramidal)  tract.  Although 
functionally  a  motor  and  therefore  a  descending  tract,  it  can 
more  easily  be  traced  from  the  oblongata  upward  to  the  higher 
centers.  It  appears  as  an  eminence  (pyramis)  on  the  ventral 
surface  of  the  oblongata  below  the  pons  near  the  midline  (cf . 
Section  95).  Its  fibers  interdigitate  with  those  of  the  pons, 
through  which  the  cortico-spinal  tract  can  be  traced.  It  can 
then  be  followed  along  the  ventral  surface  of  the  mesencepha- 
lon  through  the  pedunculus  cerebri  into  the  internal  capsule. 
These  fibers  arise  from  the  cortical  neurons  of  the  superior 
frontal  gyrus;  see  King  ('11)  and  Simpson  and  King  ('11). 

139.  Internal  capsule. — From  the  reference  books  master 
the  topographic  relations  of  the  functional  systems  of  fibers  in 
the  internal  capsule.     For  the  connections  of  these  tracts  in  the 
human  brain  see  the  following:  Barker  ('01),  pp.  666-746  and 
875-1048;  Barker  ('16),  Fig.  591,  p.  442;  Cunningham  ('15), 
Figs.  567-573,  pp.  638-643,  also  account  on  p.  642;  Herrick 
('18),  Figs.  45,  79,  80,  81,  83;  Morris  ('14),  Figs.  692-700,  pp. 
880-888;    Piersol    ('16),    Figs.    1009-1012,    pp.    1170-1174; 
Spalteholz  ('09),  Fig.  745;  Villiger  ('12),  Figs.  128-136,   pp. 
136-143. 

140.  The  dissection  of  the  cerebrum  of  the  sheep's  brain,  as 
outlined  in  the  preceding  sections,  can  be  completely  carried 
out  on  one  lateral  half  of  the  brain.     The  other  half  of  the 
specimen  can  profitably  be  used  for  a  repetition  of  the  dissec- 
tion, or  it  may  be  cut  into  a  series  of  transverse  or  longitudinal 
slices,  in  each  of  which  some  of  the  structures  already  observed 
may  be  identified. 

Some  members  of  the  class  may  slice  this  hemisphere  in  the 
transverse  plane,  others  in  the  horizontal,  and  others  in  the 
sagittal,  and  these  specimens  may  be  compared  by  all  members. 
Compare  these  sections  with  transverse  sections  of  the  human 
brain  to  be  supplied  by  the  instructor.  Poorly  preserved 
brains  which  are  of  small  value  for  dissection  by  the  method  of 
teasing  will  give  excellent  gross  sections  for  this  study.  In 
these  sections  look  particularly  for  the  continuation  of  the 
cerebral  peduncle  into  the  internal  capsule.  Make  an  especial 
study  of  the  relations  of  the  internal  capsule  to  the  adjacent 
structures,  noting  how  the  corpus  striatum  is  made  up  of  the 


114  LABORATORY   OUTLINE    OF   NEUROLOGY 

lentiform  nucleus  lying  far  laterally  and  the  caudate  nucleus 
lying  medially  and  projecting  into  the  lateral  ventricle,  while 
the  internal  capsule  appears  as  a  band  of  white  fibers  between 
these  two  centers  and  between  the  lentiform  nucleus  and  the 
thalamus.  In  transverse  and  longitudinal  sections  of  both  the 
sheep  and  the  human  brains  identify  the  chief  nuclei  of  the 
thalamus  (Herrick  ('18),  Fig.  79)  and  review  the  relations  of 
the  various  lemniscus  systems  to  these  centers  (Herrick  ('18), 
Figs.  77  and  78) .  The  medial  and  anterior  nuclei  of  the  thala- 
mus are  seen  to  be  clearly  separate  from  the  lateral  group  of 
nuclei,  including  the  lateral  and  ventral  nuclei,  the  pulvinar 
and  the  lateral  and  medial  geniculate  bodies.  The  lateral 
group  of  nuclei  constitute  the  "neothalamus,"  or  new  thalamus 
and  are  sources  of  the  thalamic  radiations  or  sensory  projection 
fibers  to  the  cortex.  The  medial  and  anterior  nuclei  belong  to 
the  old  thalamus  and  are  concerned  chiefly  with  intrinsic  thal- 
amic reflexes.  Compare  these  structures  as  they  appear  in  the 
transverse  sections  with  their  appearance  in  the  longitudinal 
dissection  of  the  left  hemisphere.  Try  to  build  up  in  your 
mind  a  three-dimensional  picture  of  the  fiber  tracts  in  the 
sheep's  brain,  as  you  have  seen  them  in  dissections  and  gross 
sections.  If  microscopic  sections  through  the  thalamus  and 
corpus  striatum  are  available,  they  should  be  studied  in  this 
connection  and  the  account  given  by  Herrick  ('18),  Chap.  X, 
should  be  read. 

11.  Optional  Dissections  of  the  Cerebrum 

141.  The  association  tracts. — The  same  specimen  upon  which 
the  dissections  outlined  in  Sections  102  to  111  were  made 
can  be  used  for  the  following  dissections  of  the  cerebrum.  The 
association  tracts  can  be  dissected  out  in  great  detail,  following 
the  procedure  directed  for  the  sheep  and  human  in  Sections  119 
and  120,  working  carefully  with  text-book  diagrams  and  de- 
scriptions of  the  chief  systems  in  mind  and  teasing  off  the  more 
superficial  systems  before  attempting  to  study  the  deeper  sys- 
tems. It  will  be  found  that  the  stronger  and  more  easily 
isolated  association  tracts  do  not  connect  the  projection  centers, 
but  the  association  centers.  In  view  of  the  fact  that  in  the 
sheep  the  association  centers  are  small  when  compared  with 


THE    MAMMALIAN   NERVOUS   SYSTEM  115 

man,  the  greater  ease  with  which  the  human  association  tracts 
can  be  isolated  by  dissection  finds  its  obvious  explanation. 

142.  The  olfactory  apparatus. — Examine  the  human  olfac- 
tory bulb  and  striae  and  compare  them  with  those  of  the  sheep. 
Dissect  the  olfactory  tracts  in  the  way  directed  for  the  sheep 
brain  in  Sections  123  to  126;  but  do  not  continue  the  dissec- 
tion as  directed  in  Section  127.  In  this  dissection  expose  the 
hippocampus  as  follows :  Lay  the  specimen  down  on  its  median 
surface  and  carefully  tease  off  the  fibers  of  the  inferior  longi- 
tudinal fasciculus  from  the  lateral  convex  surface  of  the  tem- 
poral lobe  until  the  inferior  horn  of  the  lateral  ventricle  is 
opened.  The  teasing  should  stop  at  this  point.  Now  with  a 
probe  trace  the  inferior  horn  of  the  lateral  ventricle  to  the 
anterior  end  of  the  temporal  lobe  and  follow  the  probe  with  a 
scalpel  cut,  thus  opening  up  the  inferior  horn  of  the  lateral 
ventricle.  Similarly  probe  from  the  posterior  border  of  the 
incision  just  made  backward  toward  the  occipital  pole  of  the 
hemisphere  and  follow  the  probe  with  a  scalpel  cut,  thus  open- 
ing the  posterior  horn  of  the  ventricle  in  the  occipital  lobe. 
Now  pull  apart  the  walls  of  the  lateral  ventricle  as  thus  opened 
and  locate  the  hippocampus,  a  rounded  eminence  in  the  floor 
of  the  inferior  horn  of  the  ventricle.  At  the  point  where  the 
inferior  and  posterior  horns  of  the  ventricle  join,  the  hippo- 
campus will  be  seen  to  turn  sharply  medialward.  With  a 
scalpel  follow  the  lateral  and  posterior  borders  of  the  hippo- 
campus with  a  clean  cut.  This  incision  must  be  made  care- 
fully, cutting  from  the  ventricle  directly  outward  through  the 
wall  of  the  hemisphere  to  the  brain  surface,  and  must  follow 
the  border  of  the  hippocampus  closely.  It  will  curve  around 
from  the  ventral  to  the  medial  surface  of  the  hemisphere  and 
finally  pass  through  the  splenium  of  the  corpus  callosum  into 
the  septum  pellucidum.  Remove  the  septum  pellucidum  and 
review  the  form  of  the  entire  hippocampal  formation,  including 
the  gyrus  dentatus,  fimbria,  and  corpus  fornicis.  The  floor  of 
the  inferior  horn  of  the  lateral  ventricle  is  formed  in  part  by  the 
hippocampus  and  fimbria  and  in  part  by  the  membranous 
plexus  chorioideus  of  the  lateral  ventricle.  Note  that  this 
membrane  has  two  lines  of  attachment  to  the  massive  brain 
walls,  one  to  the  free  border  of  the  fimbria  (the  tcenia  fornicis) , 


116  LABOKATORY    OUTLINE    OP   NEUROLOGY 

and  one  to  the  brain  stem  along  the  line  of  contact  between  the 
corpus  striatum  and  thalamus  (the  tcenia  chorioidea).  Be- 
tween these  two  lines  the  membrane  is  folded  into  the  ventricle, 
thus  forming  the  fissura  chorioidea.  See  the  references  cited  in 
Section  130. 

Now  repeat  on  the  human  the  directions  outlined  for  the 
sheep  in  Sections  128  and  129. 

143.  Stria  terminalis. — The  human  brain,  following  the  pro- 
cedure outlined  in  Section  132,  may  be  further  dissected  as 
follows : 

Look  into  the  lateral  ventricle,  as  already  exposed,  and  locate 
the  head  of  the  caudate  nucleus  in  the  floor  of  the  lateral  ven- 
tricle above  the  anterior  commissure.  Now  trace  the  tail 
(cauda)  of  the  caudate  nucleus  backward  into  the  inferior  horn 
of  the  lateral  ventricle  where  it  ends  in  the  vicinity  of  the  nu- 
cleus amygdalae.  Also  follow  the  stria  terminalis  (stria  or 
tsenia  semicircularis),  which  accompanies  the  ventral  border 
of  the  caudate  nucleus  for  its  entire  length.  Some  of  its  fibers 
can  be  seen  to  enter  the  anterior  commissure.  This  stria  is 
a  correlation  tract  between  the  nucleus  amygdalae  and  the  me- 
dial olfactory  area  of  the  same  and  the  opposite  side.  It 
marks  the  boundary  between  the  cerebral  hemisphere  and  the 
thalamus. 

144.  Corpus   striatum. — Remove  the  hippocampus.     Now 
pull  upward  on  the  corpus  callosum  and  upper  wall  of  the 
lateral  ventricle  so  as  to  rip  off  the  entire  roof  of  the  ventricle, 
tearing  it  free  from  the  upper  (lateral)  border  of  the  caudate 
nucleus.     The  lentiform  nucleus  (Herrick  ('18),  Fig.  45)  will 
now  be  visible  on  the  lateral  aspect  of  the  specimen,  perhaps 
still  covered  superficially  by  the  fibers  of  the  external  capsule. 

145.  Internal   capsule. — The  broken  ends  of  the  internal 
capsule  fibers  will  now  be  seen  between  the  caudate  nucleus 
and  the  lentiform  nucleus  of  the  corpus  striatum  and  between 
the  lentiform  nucleus  and  the  thalamus.     Examine  carefully 
the  relations  of  the  internal  capsule  to  the  three  gray  masses. 
See  the  list  of  references  at  the  end  of  Section  139. 

146.  Nucleus   anterior  thalami. — Locate   the   anterior  nu- 
cleus of  the  thalamus  (also  called  nucleus  dorsalis)  which  forms 
a  well-defined  eminence  at  the  anterior  end  of  the  dorsal  aspect 


THE    MAMMALIAN   NERVOUS    SYSTEM  117 

of  the  thalamus  (tuherculum  anterius  thalami),  and  into  which 
the  tractus  mamillo-thalamicus  (Vicq.  d'Azyr's  bundle)  has 
been  traced  (Section  125  (7)).  This  is  a  part  of  the  primitive 
thalamus  which,  so  far  as  known,  has  no  direct  cortical  con- 
nections; but  fibers  can  be  traced  by  careful  teasing  directly 
forward  into  the  head  of  the  caudate  nucleus. 

147.  Optic  connections. — Trace  the  optic  tract  from  the  optic 
chiasma  to  its  endings  in  the  colliculus  superior  (optic  tectum) 
on  the  one  hand  and  to  the  pulvinar  and  lateral  geniculate  body 
on  the  other.     The  tectum  opticum  is  a  mesencephalic  center 
for  the  unconscious  reflex  movements  of  accommodation  of  the 
eyes.     By  carefully  teasing  away  the  gray  mass  of  the  colli- 
culus superior,  fibers  can  be  seen  passing  down  to  the  region  of 
the  floor  of  the  aqueduct  of  Sylvius,  where  they  effect  connec- 
tions with  the  nuclei  of  the  III  and  IV  nerves  and  with  the 
fasciculus  longitudinalis  medialis.     This  fasciculus  (which  has 
already  been  dissected  out — see  Section  109)  is  a  general  corre- 
lation tract  for  the  eye-muscle  nerves  and  for  all  visual  reflexes. 
Dissect  the  optic  radiations  from  the  pulvinar  to  the  occipital 
pole  of  the  cerebral  hemisphere.     These  fibers  swing  outward, 
then  dorsalward  and  backward  into  the  cuneus,  passing  up 
behind  the  internal  capsule  fibers. 

148.  Auditory  connections. — The  auditory  path  has  already 
been  traced  (Section  106)  by  way  of  the  lateral  lemniscus  to  its 
thalamic  nucleus,  the  medial  geniculate  body.     Remove  the 
optic  tract  and  pulvinar  carefully.     Then  tease  the  fibers  from 
the  medial  geniculate  body  upward  into  the  internal  capsule. 
They  run  just  in  front  of  the  optic  radiations  and  end  in  the 
temporal  lobe  of  the  cortex. 

149.  Somesthetic  radiations. — Carefully  tease  the  lateral  and 
medial  lemniscus  fibers  from  the  midbrain  region,  into  which 
they  have  been  traced  (Sections  106  and  108),  upward  into 
the  thalamus.     Their  terminal  nuclei  comprise  the  lateral  and 
ventral  nuclei  of  the  thalamus,  lying  internally  of  the  pulvinar. 
From  these  nuclei  strands  of  fibers  can  be  torn  upward  toward 
the  cortex  into  the  internal  capsule.     These  are  the  somatic 
sensory  radiations  destined  for  the  gyms  centralis  posterior. 

150.  Pyramidal  tract.  —  Next  tear  the  pyramidal  tract  up- 
ward from  the  midbrain  floor  along  the  cerebral  peduncle  into 


118  LABORATORY    OUTLINE    OF    NEUROLOGY 

the  internal  capsule.     These  are  descending  fibers  from  the 
gyrus  centralis  anterior. 

151.  Brachium  Conjunctivum. — Finally,  tear  the  fibers  of  the 
brachium  conjunctivum  downward  to  their  decussation  under 
the  aqueduct  of  Sylvius.     The  red  nucleus  or  nucleus  ruber 
(where  these  fibers  end  after  decussating)  will  be  seen  imme- 
diately in  front  (cephalad)  of  this  decussation,  as  a  round  gray 
mass  about  the  size  of  a  pea,  not  far  from  the  median  plane. 
Its  rubro-thalamic  tracts  can  readily  be  seen  by  teasing  for- 
ward from  the  nucleus. 

12.  Recapitulation  of  Conduction  Paths 

152.  Thalamic  Nuclei. — Now  make  a  list  of  the  nuclei  of  the 
diencephalon  which  you  have  seen  and  tabulate  their  fiber 
connections. 

153.  Finally,  having  completed  the  Table  of  Conduction 
Pathways  (Section  101)  and  a  table  or  diagram  of  the  olfactory 
tracts  (Section  130),  make  a  systematic  review  of  each  func- 
tional system  of  tracts.     For  each  system  get  a  clear  picture  of 
the  course  of  the  nervous  impulses  involved  in  both  the  reflex 
and  the  cortical  functioning  of  that  system.     With  the  intact 
human  brain  before  you,  try  to  visualize  the  courses  of  the 
fiber  tracts  in  question  with  reference  to  the  external  land- 
marks. 


V.  LITERATURE 

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HERRICK,  C.  JUDSON.  1899.  The  Cranial  and  First  Spinal  Nerves  of 
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— .  1903.  The  Organ  and  Sense  of  Taste  in  Fishes,  Bui.  U.  S. 
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— .  1908.  On  the  Phylogenetic  Differentiation  of  the  Organs  of 
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HERRICK,  C.  JUDSON,  and  COGHILL,  G.  E.  1915.  The  Development 
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LITERATURE  123 

MONAKOW,  C.  VON.  1914.  Die  Legalisation  im  Grosshirn  und  der 
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MORRIS.  1914.  Human  Anatomy,  Part  III,  The  Nervous  System, 
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NORRIS,  H.  W.,  and  HUGHES,  SALLY  P.  1919.  Cranial  Nerve  Com- 
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OBERSTEINER,  HEINRICH.  1912.  Anleitung  beim  Studium  des  Baues 
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PARKER,  G.  H.  1903.  The  Sense  of  Hearing  in  Fishes,  Am.  Nat- 
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PARKER,  G.  H.,  and  VAN  HEUSEN,  ANNE  P.  1917.  The  Reception  of 
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PARKER,  G.  H.,  and  SHELDON,  R.  E.  1913.  The  Sense  of  Smell  in 
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PARKER,  T.  J.  1900.  A  Course  of  Instruction  in  Zootomy  (Verte- 
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PARKER,  T.  J.,  and  HASWELL,  W.  1910.  Text-book  of  Zoology, 
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PEABODY,  J.  E.  1897.  The  Ampullae  of  Lorenzini  of  the  Selachii, 
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RAMON  Y  CAJAL,  S.  1909-1911.  Histologie  du  Systeme  nerveux,  2 
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RAUBER  and  KOPSCH,  FR.  1912.  Lehrbuch  der  Anatomie  des  Men- 
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RIDDOCH,  GEORGE.  1917.  The  Reflex  Functions  of  the  Completely 
Divided  Spinal  Cord  in  Man,  Compared  with  those  Associated  with  Less 
Severe  Lesions,  Brain,  vol.  40,  pp.  264-402. 

VAN  RYNBERK,  G.  1907-1908.  Die  neueren  Beitrage  zur  Anatomic 
und  Physiologic  des  Kleinhirns  der  Sauger  (critical  review),  Folia 
Neurobiologica,  Bd.  I,  pp.  46-62,  403-419,  53^551. 

.     1912.     Weitere  Beitrage  zum  Localizationsproblem  im  Klein- 

hirn  (critical  review),  Folia  Neurobiol.,  Bd.  6,  Supplement,  pp.  143-170. 

SABIN,  FLORENCE.  1901.  An  Atlas  of  the  Medulla  and  Midbrain, 
Friedenwald  Co.,  Baltimore. 

SCHAEFER,  E.  A.     1900.     Physiology,  London. 

SHAMBAUGH,  G.  E.  1907.  A  Restudy  of  the  Minute  Anatomy  of 
Structures  in  the  Cochlea  with  Conclusions  Bearing  on  the  Solution  of  the 
Problem  of  Tone  Perception,  Am.  Jour.  Anat.,  vol.  7,  pp.  245-258. 

.     1908.     The  Membrana  Tectoria  and  the  Theory  of  Tone 

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SHELDON,  R.  E.  1909.  The  Phylogeny  of  the  Facial  Nerve  and 
Chorda  Tympani,  Anat.  Rec.,  vol.  3,  pp.  593-617. 

— .     1909a.     The  Reactions  of  Dogfish  to  Chemical  Stimuli,  Jour. 
Comp.  Neur.,  vol.  19,  pp.  273-311. 

.     1911.     The  Sense  of  Smell  in  Selachians,  Jour.  Exp.  Zool., 

vol.  10,  pp.  51-62. 

.     1914.     Paraffine-Weigert    Methods    for    the    Staining    of 

Nervous  Tissue,  with  some  new  Modifications,  Folia  Neurobiol.,  Bd.  8, 
pp.  1-28. 

SHERRINGTON,  C.  S.  1906.  The  Integrative  Action  of  the  Nervous 
System,  New  York. 

SIMPSON,  S.,  and  KING,  J.  LUELLA.  1911.  Localization  of  the  Motor 
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SMITH,  G.  ELLIOT.  1903.  Further  Observations  on  the  Natural  Mode 
of  Subdivision  of  the  Mammalian  Cerebellum,  Anat.  Anz.,  Bd.  23,  pp. 
368-384. 

.     1907.     A  New  Topographical  Survey  of  the  Human  Cerebral 

Cortex,  Jour.  Anat.  and  Physiol.,  vol.  41,  pp.  237-254. 

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STARLING,  ERNEST  H.  1915.  Principles  of  Human  Physiology,  2d 
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STARR,  M.  A.,  STRONG,  O.  S.,  and  LEAMING,  E.  1896.  Atlas  of  Nerve 
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LITERATURE  125 

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VILLIGER,  E.     1912.     Brain  and  Spinal  Cord  (translated  by  G.  A.  Pier- 
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WEED,  LEWIS,  H.     1914.     Studies  on  Cerebrospinal  Fluid,  Jour.  Med. 
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Lower  Portion  of  the  Human  Brain  Stem,  Carnegie  Inst.  of  Washington, 
Pub.  No.  191. 

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Pig  and  in  Man,  Carnegie  Inst.  of  Washington,  Pub.  No.  225. 

WIEDERSHEIM,  ROBERT.     1907.     Comparative  Anatomy,  3d  English 
edition,  London. 

WILSON,  J.  G.     1905.     The  Structure  and  Function  of  the  Taste-buds 
of  the  Larynx,  Brain,  Part  CX,  vol.  28,  pp.  339-351. 

WINKLER,  C.,  and  POTTER,  ADA.     1911.     An  Anatomical  Guide  to  Ex- 
perimental Researches  on  the  Rabbit's  Brain,  Amsterdam. 

— .  1914.  An  Anatomical  Guide  to  Experimental  Researches 
on  the  Cat's  Brain,  Amsterdam. 


INDEX 


The  references  are  to  pages.  Numbers  printed  in  black-face  type  re- 
fer to  pages  with  illustrations.  A  Glossary  of  the  more  commonly  used 
neurological  terms  is  combined  with  the  Index  of  the  senior  author's 
Introduction  to  Neurology. 


ACOUSTIC    apparatus.     See    Audi- 
tory apparatus. 

Acoustico-lateral   system,    20,  21, 
23-26,  32,  33,  36 

Ala  cinerea,  54,  67,  76,  77,  98 

Ala  lobuli  centralis,  86 

Amygdala,  105,  111,  116 

Aqueduct  of  Sylvius,  38,  56,  99 

Arbor  vitse,  66,  85 

Archipallium,  99,  109 

Area  acustica,  54,  55 
olfactoria,  56,  104-106 
parolfactory,  of  Broca,  105 

Auditory    apparatus,    of    dogfish, 

18,  20,  21,  35 
of  mammal,  72,  112,  117  • 

BETWEENBRAIN.  See  Diencephalon. 
Black   substance.     See   Substantia 

nigra. 

Blood  vessels  of  brain,  47 
Brachium,  of  colliculus  inferior,  58, 
100,  112 

conjunctivum,  58,  82-84,  95,  118 

pontis,  57,  58,  82r84,  94 

quadrigeminum  inferius,  58,  100, 

112 
Brain  of  dogfish,  18,  20,  21,  35-38 

of  fetal  pig,  45 

methods  of  dissection,  43,  44 

of  sheep,  48,  50,  52,  56,  57,  68 
removal  of,  39 

stem,  51,  99 

subdivisions  of,  45 
Broca,  area  parolfactoria  of,  105 

convolution  of,  100 

diagonal  band  of,  60,  107 
Bulb,  olfactory,  20,  21,  48,  60,  56, 

99,  104,  115 


CAPSULE,  external,  116 

internal,  111,  113,  114,  116 
Centers,  association,  114 

projection,  114 
Cerebellum,  36,  37,  51,  82-89 

localization  in,  86-88 
Cerebrum,  37,  51,  99,  114 
Chiasma,  optic,  60,  66,  112,  117 
Cingulum,  102,  103 
Clarke's  column.     See  Nucleus  tho- 

racalis. 

Clava,  55,  57,  58,  70 
Cochlea,  72 
Colliculus  facialis,  53,  67 

inferior,  57,  58,  96,  99,  112 

superior,  56-58,  99,  112,  117 
Columna      fornicis.     See    Fornix, 

column  of. 

Columns  of  spinal  cord,  64 
Commissura,    anterior,     56,    105, 
116 

habenularum,  56 

hippocampi,  109 

posterior,  66 

superior.     See  Commissura  hab- 
enularum. 
Components    of    cranial    nerves, 

24-26,  29,  30,  49 
Corona  radiata,  103 
Corpus  callosum,  56,  102 

fornicis.     See  Fornix,  body  of. 

geniculatum  laterale.     See  Genic- 

ulate  body,  lateral. 
mediale.     See  Geniculate  body, 
medial. 

mamillare.     See  Mammillary 
body. 

pineale,  18,  66,  67 

restiforme.    See  Restiform  body. 


127 


128 


INDEX 


Corpus  striatum,  113,  116 

trapezoideum.     See      Trapezoid 

body. 

Cortex,  cerebellar,  51,  85 
cerebral,  36,  51,  99,  101 
Corti,  organ  of.     See  Spiral  organ. 
Culmen  monticuli,  56,  86,  87 
Cuneus,  100,  117 
Cutaneous  system  of  dogfish,  20, 

21,  35 
of  mammal,  68 


DECLIVE  monticuli,  66,  86,  87 
Dependencies,  cortical,  46 
Diencephalon,  37,  99,  118 
Dogfish,  16-38 

EAB  of  dogfish,  18,  19,  20,  21 

of  mammal,  72 
Eminentia  abducentis,  53 

medialis,  53 

Endbrain.     See  Telencephalon. 
Ependyma,  64 
Epiphysis.     See  Pineal  body. 
Epithalamus,  20,  37 
Exteroceptive  systems,  66,  72 
Eye  of  dogfish,  18,  20,  27 

of  mammal,  28 


FASCIA  dentata,  109 
Fasciculus,       cerebro-spinal.     See 
Tract,  pyramidal. 

cuneatus,  55,  67,  68,  70,  97 

gracilis,  55,  67,  70,  97 

lateralis,  68 

longitudinalis  inferior,  103 
medialis,  35,  76,  80,  98,  117 
superior,  103 

occipito-frontalis  inferior,  103 

retro  flexus,  107 

solitarius,  54,  76,  98 

of  spinal  cord,  64 

transversus  occipitalis,  103 

uncinatus,  103 
Fibers  (fibrse),  arcuate,  79,  84,  102 

associational,  102,  103,  114 

profundae  pontis,  94 

projection,  114 

superficiales  pontis,  94 
Fillet.     See  Lemniscus. 
Fimbria,  109,  115 
Fish,  nervous  system  of,  16-38 


Fissure  (fissura),  ansata,  52,  56 

calcarine,  100 

central,  100 

chorioidea,  116 

collateral,  100 

crucial,  52,  56 

hippocampal,  101,  109 

lateral,  100 

preculminata,  88 

primaria,  88 

rhinalis,  50 

of  Rolando,  100 

secunda,  56,  86,  88 

of  Sylvius,  100 
Flocculus,  48,  52,  85 
Folium  vermis,  87 
Foramen,  interventricular,  38,  56, 
57 

of  Monro.     See  Foramen,  inter- 
ventricular. 
Formatio  reticularis.     See  Reticu- 

lar  Formation. 
Fornix,  108-110 

body  of,  56,  109 

column  of,  66,  109,  110 
Fossa  rhomboidea.     See  Ventricle, 

fourth. 
Fovea  inferior,  54,  57 

superior,  54,  57 
Funiculus  of  spinal  cord,  64,  70 

teres,  53,  57 

GANGLION,    gasserian.     See    Gan- 
glion, semilunar. 

geniculate,  76 

jugular,  X,  68 

nodosal  X,  76 

petrpsal  IX,  76 

semilunar,  68 

spinal,  47 

superior  IX,  68 
Geniculate  body,  lateral,   57,  99, 

112,  117 

medial,  57,  68,  97,  99,  112,  117 
Gills  of  dogfish,  17, 18,  20,  34,  37 
Gustatory  apparatus.     See  Taste. 
Gyrus,  centralis,  100 

cinguli,  56,  100 

dentatus,  56,  109 

frontalis,  100 

hippocampi,  99,  101 

lateral  olfactory,  105 

subcallosus,  105 

temporalis,  101 


INDEX 


129 


HABENULA,  56,  67,  106 
Heart  of  dogfish,  17 
Hemisphere,  cerebellar,  62,  85,  95 
cerebral,  20,  21,  37,  99,  100,  101 
Hippocampus,  108,  109,  115 
Hypophysis.     See  Pituitary  body. 
Hypothalamus,  37 

INDUSIUM,  108 
Infundibulum,  50,  56 
Insula,  100 
Island  of  Reil,  100 
Isthmus,  37,  51 

LAGENA  of  dogfish,  19 
Lamina  epithelialis,  59 

quadrigemina,  66 

terminalis,  66,  57 
Lateral  line  organs  and  nerves,  17, 

Lemniscus,  definition  of,  72 

lateral,  58,  73,  74,  96,  97,  117 

medial,  70,  71,  97,  98 

spinal,  66,  71 

trigeminal,  69 

visceral,  79 
Lingula,  87 
Lobe  (lobus),  anterior  cerebelli,  86 

frontal,  100 

occipital,  100 

parietal,  100 

pyriform,  48,  50,  99 

temporal,  100,  108 
Lobulus  ansiformis,  86 

biventer,  86 

centralis,  86,  87 

paramedianus,  86 

quadrangularis,  86 

semilunaris,  86 

simplex,  86 

Localization,  cortical,  62,  101 
Longitudinal  medial  bundle.     See 

Fasciculus,  longitudinal  medial 
Lyra,  109 

MAMMiLLARYbody,  50,  66,  106 

^assa  intermedia  66 

Medulla  oblongata,  correlation  in 

78 

of  dogfish,  20,  26,  35,  36,  37 
of  mammal,  50,  52,  53,  56,  67 
reference  to  figures  of,  60 
spinalis.     See  Spinal  cord. 
Membranes  of  brain.     See   Men- 
inges. 
9 


Meninges,  21,  46,  47 
Mesencephalon,  37,  99 

reference  to  figures  of,  61 
Meynert's  bundle,  107 
Midbrain.     See  Mesencephalon 
Mitral  cells,  104 
Muscles  of  eyeball,  18,  21 
Mustelus  canis,  16-38 

NASAL     organ     and     nerve.     See 

Olfactory. 
Neopallium,  99 
Neothalamus,  114 
Nerve,  abducens,  31 
accessory,  32 
acoustic,  31,  73 
auditory.     See  Nerve,  acoustic. 
cochlear,  central  connections  of 

73 

cranial,  49 

of  dogfish,  18, 20, 21,  23-26,  28-34 
facial,  31 

glossopharyngeal,  31 
hypoglossal,  32 
of  Lancisius,  108 
of  lateral  lines,  20,  21,  23-26 
oculomotor,  31 
olfactory,  30 
optic,  30 

spinal,  of  fetal  pig,  46 
terminal,  20,  24,  30,  49 
trigeminal,  31 

central  connections  of,  68,  69 
trochlear,  31 
vagus,  31 
vestibular,    central    connections 

of,  75 
Neuron,  63 
Nodulus,  56,  86,  87 
Nucleus,  ambiguus,  77 
amygdalae,  105,  111,  116 
anterior  thalami,  107,  116 
arcuate,  84 

caudate,  111,  114,  116 
of  cerebellum,  84 
cochlear,  55,  57,  58,  73,  74,  96 
dentate,  84 
dorsalis  Clarkii,  64 
dorsal  X,  77,  98 
emboliformis,  85 
of  fasciculus  cuneatus,  97 
gracilis,  97 
solitarius,  76 
fastigii,  85 


130 


INDEX 


Nucleus,  globosus,  85 
of  III  nerve,  77 
lateral  olfactory,  48,  60,  105 

of  thalamus,  114,  117 
lentiform,  111,  114,  116 
motor  V,  69,  77 

VII,  77 
pontis,  84,  95 
red,  96,  118 
ruber,  96,  118 
salivatory,  77 
sensory  V,  69 
of  spinal  V  tract,  69 
thoracalis,  of  Clarke,  64 
ventral  of  thalamus,  114,  117 
vestibular,  55,  57,  68,  75,  96 

OBEX,  57 

Olfactory    apparatus,    of    dogfish, 

18,  20,  21,  24,  25,  35 
of  mammal,  104-110,  115,  116 
organ,  104 
Olive,  inferior,  84 

superior,  73,  75,  96,  97 
Operculum,  100 
Optic  apparatus  of  dogfish,  18,  20, 

21,  27,  35 

of  mammal,  112,  117 
chiasma,  50,  66,  112,  117 
lobes,  37 
Optocoele,  38 

PALLIUM,  99 

Paraflocculus,  48 

Peduncle,  cerebellar,  51,  82-84 

inferior.     See     Corpus     resti- 

forme. 

medial.     See  Brachium  pontis. 
superior.     See  Brachium  con- 

junctivum. 

cerebral,  37,  50,  66,  68,  95 
of  corpus  callosum,  105 
of  inferior  colliculus,  100 
Pig,  fetal,  brain  of,  45 
spinal  cord  of,  45 

nerves  of,  45 
Pineal  body,  18,  66,  67 
Pituitary  body,  56 
Plexus,   choroid,   definition  of,   59 
of  fourth  ventricle,  52,  66,  58 
of  lateral  ventricles,  59,   111, 

115 
of  third  ventricle,  56,  58 


Pons,  48,  50,  66,  68,  85 

Posterior      longitudinal      bundle. 

See       Fasciculus,       longitudinal 

medial. 

Proprioceptive  systems,  66,  72,  85 
Pulvinar,  100,  112,  117 
Pyramid,  60,  68,  113 
Pyramis  cerebelli,  56,  86,  87 


RADIATIONS,  auditory,  117 

optic,  117 

somesthetic,  117 

thalamic,  114 
Recess,  cerebellar,  66,  58 

lateral,  of  fourth  ventricle,  53 

preoptic,  56 

Reference  books,  14,  15;  119-125 
Restiform  body,  57,  58,  82,  83,  93 
Reticular  formation,  64,  72,  79,  96 
Retina,  111 
Rhinencephalon,  104 
Rhomb  encephalon,  37,  51,  99 
Root,  cochlear,  73,  96 

mesencephalic  V,  69 

vestibular,  96 
Rostrum  corporis  callosi,  66 


SEGMENT AL  apparatus,  51,  99 
Sense  organs  of  fishes,  16,  17 

of  somatic  sensory  systems,  67 
Septum  pellucidum,  56,  105 
Shark,  16-38 
Skate,  16 
Smell,  apparatus  of.     See  Olfactory 

apparatus. 
Somatic  motor  system,  17,  24-26, 

29,  30,  35,  37,  53,  66,  78 
sensory  system,   17,  24-26,  29, 

30,  36,  37,  54,  66,  67 

Space,  anterior  perforated,  99,  105, 

106 

Spinal  cord  of  fetal  pig,  46 
functions  of,  65 
human,  47,  64 
neurons  of,  63-65 
sequence  of  myelination  in,  67 
Spiracle,  18,  20,  21,  25 
Spiral  organ,  72 
Squalus  acanthias,  16-38 
Stria  of  Lancisius,  108 

longitudinalis  median's,  108 
medullares  acusticae,  73,  96 


INDEX 


131 


Stria  medullares,  thalami,  66, 106, 
110 

olfactory,  104,  105,  115 

semicircularis,  106,  111 

terminalis,  105,  106,  111,  116 
Substantia  alba,  64 

gelatinosa,  64,  69 

grisea,  64 

nigra,  84 
Sulcus,  cinguli,  56,  100 

furcal,  86 

horizontal,  86,  88 

limiting,  36,  37,  54 

postcentralis,  88 

postclivalis,  86 

postnodularis,  88 

postpyramidalis,  88 

precentralis,  88,  100 

preclivalis,  86,  88 

prepyramidalis,  88 

primarius,  56,  85,  86,  88 

temporal,  100 

uvulo-nodularis,  86,  88 
Suprasegmental  apparatus,  51,  99 
Sympathetic  nervous  system,  46, 

67 


T^ENIA  chorioidea,  116 

fornicis,  115 

of  fourth  ventricle,  52,  57 

semicircularis,  106,  111,  116 

thalami,  57,  59 

of   third   ventricle.     See   Tcenia 
thalami. 

ventriculi     tertii.      See     Toenia 

thalami. 
Taste,  bulbar  center  of,  76 

nerves  of,  77 

organs  of,  77 
Tectum,  optic,  112,  117 
Tegmen  fossae  rhomboideae,  58 
Tegmentum,  96 
Telencephalon,  37,  99 
Thalamus,  21,  37,  57,  99,  114,  118 

reference  to  figures  of,  61 
Tonsilla,  86 

Tract  (tractus),  associational,  102, 
103,  114 

central  tegmental,  84 

cerebello-tegmental,  96 

cerebro-spinal.      See    Tract,   py- 
ramidal. 

cortico-pontile,  85,  95 


Tract  (tractus),  cortico-spinal.   See 

Tract,  pyramidal. 
of    Flechsig.     See   Tract,   spino- 

cerebellar,  dorsal. 
general  somatic  sensory,  72    • 
of    Gowers.     See    Tract,    spino- 

cerebellar,  ventral. 
habenulo-peduncular,  107 
mamillo-peduncular,  107 
mamillo-tegmental,  107 
mamillo-thalamic,  107,  117 
olfactory,  50,  104,  115 
olfactory  projection,  106 
olfacto-cortical,  108 
olfacto-habenular,  106 
olfacto-mammillary,  106 
olfacto-tegmental,  106 
olivo-cerebellar,  84 
optic,  50,  100,  112,  117 
projection,  114 
pyramidal,  80,  81,.  95,  99,  112, 

spinal  trigeminal,  57,  58,  68 

spino-bulbar,  79 

spino-cerebellar,  dorsal,  57,  58, 

83,  94 
ventral,  84,  96,  97 

taeniae,  106 

thalamo-mammillary,  107 

of  Vicq  d'Azyr,  107,  117 

rubro-thalamic,  118 
Trapezoid  body,  48,  50,  56,  58,  73, 

75,  96 
Trigonum  hypoglossi,  53,  57 

vagi,  54 
Tuber,  cerebelli,  86 

cinereum,  50 

vermis,  87 
Tuberculum  acusticum,  55,  73 

anterius  thalami,  117 

cinereum,  55,  68 

cuneatum,  55,  57,  58,  70 

olfactorium,  50,  56,  99,  105,  106 

UNCUS,  101, 105, 108 
Uvula,  56,  86,  87 

VELUM,  anterior  medullary,  52,  66, 

58,  95 

posterior  medullary,  58 
Ventricle,    first   and   second.     See 

Ventricle,  lateral. 
fourth,  20,  35,  36,  37,  38,  51,  53, 
56 


132 


INDEX 


Ventricle,    lateral,    38,    110,    111, 

115 

third,  38,  66,  57,  99 
Vermis  cerebelli,  48,  62,  85 
Visceral    apparatus,     of    dogfish, 
20,  21 


Visceral  motor  system,  17,  24-26, 

29, 30,  36,  37,  53,  66,  77 
sensory  system,   17,  24-26,   29, 

30,  36,  37,  53,  66,  76 
Visual  apparatus.     See  Optic  ap- 
paratus. 


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